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Am J Physiol Heart Circ Physiol 291: H1360-H1370, 2006. First published March 24, 2006; doi:10.1152/ajpheart.01326.2005
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Synergistic activation of salmon cardiac function by endothelin and beta-adrenergic stimulation

Heidi Vierimaa,1 Jarkko Ronkainen,1 Heikki Ruskoaho,2 and Olli Vuolteenaho1

Departments of 1Physiology and 2Pharmacology and Toxicology, Biocenter Oulu, University of Oulu, Oulu, Finland

Submitted 16 December 2005 ; accepted in final form 14 March 2006


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The aim was to find out the effects of endothelin-1 (ET-1) in salmon (Salmo salar) cardiac contractile and endocrine function and its possible interaction with beta-adrenergic regulation. We found that ET-1 has a positive inotropic effect in salmon heart. ET-1 (30 nM) increased the contraction amplitude 17 ± 4.7% compared with the basal level. beta-Adrenergic activation (isoprenaline, 100 nM) increased contraction amplitude 30 ± 13.1%, but it did not affect the contractile response to ET-1. ET-1 (10 nM) stimulated the secretion of salmon cardiac natriuretic peptide (sCP) from isolated salmon ventricle (3.3 ± 0.14-fold compared with control) but did not have any effect on ventricular sCP mRNA. Isoprenaline alone (0.1–1,000 nM) did not stimulate sCP release, but ET-1 (10 nM) together with isoprenaline (0.1 nM) caused a significantly greater increase of sCP release than ET-1 alone (5.4 ± 0.07 vs. 3.3 ± 0.14 times increase compared with control). The effects on the contractile and secretory function could be inhibited by a selective ETA-receptor antagonist BQ-610 (1 µM), whereas ETB-receptor blockage (by 100 nM BQ-788) enhanced the secretory response. Thus ET-1 is a phylogenetically conserved regulator of cardiac function, which has synergistic action with beta-adrenergic stimulation. The modulatory effects of ET-1 may therefore be especially important in situations with high beta-adrenergic tone.

natriuretic peptide; cardiac contractile function

ENDOTHELIN-1 (ET-1) is a peptide produced by the vascular endothelium and several other tissues, such as the central nervous system and kidney (53, 77). ET-1 is mainly released from the endothelial cells abluminally (37), and it appears to function as a local paracrine regulator, not as a circulating hormone. ET-1 is a potent vasoconstrictor that elevates the blood pressure (77) and contributes to the maintenance of basal vascular tone (22). The physiological effects of ET-1 are mediated by at least two subtypes of ET receptors, ETA and ETB, which are expressed in the atrial and ventricular myocardium as well as in the atrioventricular conducting system and endocardial cells (47).

ET-1 has been found to have positive inotropic effects mediated by ETA receptors (33) that are linked via Gq-type G protein to phospholipase C (27, 37, 38, 49). The role of ETB receptors in cardiac regulation is not known, although activation of both receptor types has been reported to be associated with positive inotropic effects (31, 33, 54, 77). The inotropic effects seem to be due to the sensitization of the myocytes to intracellular calcium, which in turn results from increased activity of the sodium-proton exchanger and intracellular alkalinization (32, 39) and increased amplitude of Ca2+ transients (73).

ET-1 stimulates the secretion of atrial natriuretic peptide (ANP) (14, 18, 56) and augments the stimulatory effect on ANP release of volume expansion (14, 20) and stretch (57), apparently by an ETA-mediated effect (59). We have shown in the rat that the release of ANP induced by volume expansion can be inhibited by the administration of a combined ETA/ETB-receptor antagonist (41). ET-1 appears to have a role in the pathophysiology of various heart diseases (38).

The beta-adrenergic system is a major regulator of cardiac function. Stimulation of the adrenergic pathways has been suggested to induce alterations in the signal transduction of other cardiovascular systems, such as the ET-receptor pathways (76). It seems likely that cardiac function is regulated by cross talk among several endogenous regulators, such as ET-1 and beta-adrenergic activation. The potential connection between ET-1 and adrenergic stimulation in the regulation of cardiac contractile function in vitro (8) and in vivo (35), as well as the effects of ET-1 and adrenergic stimulation on cardiomyocyte Ca2+ currents (68, 75), has been studied in mammals. The results indicate that cardiac contractility can be regulated either positively or negatively by ET-1 and adrenergic stimulation, depending, such as, on the concentration of norepinephrine (8). The cross talk between ET-1 and beta-adrenergic activation in cardiac endocrine function is not known.

The natriuretic peptides are a conserved hormone family, members of which can be found from primitive vertebrates to mammals (25, 29, 30, 67). We recently discovered in salmon (Salmo salar) a novel natriuretic peptide hormone, salmon cardiac peptide (sCP), that can serve as a marker of cardiac endocrine function (36, 42, 65–67, 72). The physiological effects, structure, and regulation of sCP and its gene resemble those of mammalian natriuretic peptides (65). The regulation of its secretion and gene expression (36, 65, 72) and comparative structural analyses (26, 63, 64, 69) indicate that sCP is an ANP-like peptide. Whereas mechanical load appears to be the key inducer of sCP release (36, 65), ET-1 can stimulate sCP secretion in vivo (72). Whether the effects of ET-1 on salmon heart are direct or caused by hemodynamic changes is not known. In the present study we wanted to find out the role of ET-1 in salmon cardiac function and the possible interactions between two major regulators of cardiac function, ET-1 and beta-adrenergic stimulation. We have now tested these ideas by monitoring perfused isolated salmon myocardium contractile function and by measuring sCP secretion from salmon heart in response to ET-1 and beta-adrenergic stimulation.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Experimental animals. Salmon (Salmo salar) of either sex, weighing 229 ± 9.38 g (series 1, contractility experiments in myocardial strip preparations; mean ± SE), 462 ± 14.5 g (series 2, perfusion experiments with sCP measurements), and 456 ± 11.5 g (series 3, perfusion experiments with contractility and sCP measurements), were purchased from the hatcheries of the Finnish Game and Fisheries Institute in Taivalkoski, Muonio, and Laukaa, Finland, and from the hatchery of Imatran Voima power plant in Muhos, Finland. They were kept without feeding at the Department of Physiology for up to 14 days in a 1,500-liter tank circulated with aerated water at 6°C under a light-dark cycle appropriate for the season (12-h:12-h light-dark during the autumn; and 9-h:15-h light-dark during the winter). No more than 30 fish were kept in the tank at a time. Plasma levels of catecholamines have previously been shown to return to near baseline 24 h after acute stress (21). Therefore, the fish were kept in the tank for at least 24 h before use. The fish appeared healthy, and their behavior was normal (not excited or agitated) at the start of the experiments. The experiments were approved by the Animal Experimentation Review Board of the University of Oulu.

Experimental protocol for contractility measurements in myocardial strip preparations: series 1. In the first set of experiments, the contractile function of salmon heart was studied by using a simple ventricular strip preparation. Myocardial strips were prepared by cutting salmon ventricle in half. One half was used as control for mRNA measurements. The other half was mounted in an organ chamber, attached to a force transducer (F10 type 375, Hugo Sachs Electronics), and superfused with 10°C modified Cortland saline containing (in mmol) 124 NaCl, 5 CaCl2·2H2O, 3 KCl, 0.09 NaH2PO4·H2O, 1.8 Na2HPO4·2H2O, 1.1 MgSO4·7H2O, 5.6 dextrose, and 12 NaHCO3 (gassed with 95% O2-5% CO2; 240 mosm/kgH2O) at 1.5 ml/min (17). The muscle strips were electrically stimulated by field stimulation (0.25 Hz). The preparations were allowed to equilibrate for 30 min at a low preload. Thereafter, they were gradually stretched to the optimal length (Lmax) at which the developed force attained a maximum. The Frank-Starling responses were determined in one group of muscle strips to characterize the contractile function (n = 5). In the remaining groups, the final preload was adjusted to 50% of the force at Lmax.

In the first group (n = 5), after an equilibration period of 30 min, the concentration of human ET-1 (Peninsula Laboratories Europe, Merseyside, UK) in the perfusion buffer was cumulatively increased every 30 min from 1 to 3, 10, 30, and 100 nM. Human peptide was used because the structure of fish ET-1 is not known. A peptide closely homologous to human ET-2 has been characterized from trout kidney (74). However, trout vessels appear to be more sensitive to mammalian ET-1 than the trout ET-2-like peptide (23, 74). In the second group (n = 7), responses to ET-1 were tested as described above, except for the presence of BQ-610 (Bachem, Bubendorff, Switzerland). BQ-610 (125 nM) was added in perfusion buffer 30 min before the first ET-1 dose. The third group (n = 6) acted as a positive control (isoprenaline). After a control period (210 min), the dose-response curves for isoprenaline were determined to see how well the inotropic reserve had been preserved. The isoprenaline concentration in the perfusion buffer was cumulatively increased every 10 min from 0 to 0.1, 1, 10, 100, 1,000, and finally to 10,000 nM. Finally, the fourth group (n = 10) acted as a control group (without any treatment).

The following parameters were analyzed: contraction amplitude, time to peak developed force, duration, time from peak force to 50% relaxation, and time from peak force to 90% relaxation.

Isolated salmon ventricle perfusion. We have previously described the salmon ventricle perfusion system in detail (36). Briefly, the salmon was euthanized, and the beating ventricle was placed in an organ bath. The ventricle preparation was paced by a focal stimulus and perfused with a modified version of Cortland saline, and perfusate samples were collected. The mechanical load of the ventricle can be altered by adjusting the outflow height. The samples were stored at –20°C for use in the radioimmunoassays. The ventricles were stored at –70°C for the measurement of sCP mRNA by quantitative RT-PCR.

Perfusion experiments with sCP measurement: series 2. In the second set of experiments, the role of ET in sCP secretion was studied using the perfusion system (36). The ventricle was paced by a focal stimulus (0.25 Hz) and perfused with a flow rate of 4 ml/min with a modified version of Cortland saline. The perfusate was collected in 1-min fractions. Basal samples were collected during the first 5 min. Thereafter, mechanical load (13 cmH2O) was applied with or without ET-1 (5 nM; n = 8 and 7, respectively). In the third group, ET-1 was added without any mechanical load (n = 7). ET-1 was present in the perfusion buffer during the whole experiment. In the fourth group (n = 8), the selective ETA-receptor antagonist BQ-610 (125 nM) was added in the perfusion buffer at the time the mechanical load was applied, and samples were collected during the next 20 min. Finally, samples were collected during the last 15 min without the mechanical load. The fifth group acted as the control group (n = 4). The samples were stored at –20°C for use in the radioimmunoassays. The ventricles were stored at –70°C for the measurement of sCP mRNA by quantitative RT-PCR.

Perfusion experiments with simultaneous contractility and sCP measurements: series 3. The last set of experiments was planned to study the role of ET-1 and possible interactions of ET-1 and beta-adrenergic stimulation in both cardiac contractile and endocrine function and the contribution of ETA and ETB receptors using the same perfusion setup. In this series, the contraction force (pressure generated by contraction) was recorded concomitantly with the sampling of perfusate. The contraction force was measured by recording the pressure in the lumen of the ventricle. Because of the expected chronotropic effect of isoprenaline, the ventricle preparation was paced at a higher physiological frequency (0.6-Hz focal stimulus) and perfused with a flow rate of 2 ml/min with a modified version of Cortland saline (gassed with 99.5% O2-0.5% CO2). The perfusate was collected in 5-min fractions. Basal samples were collected during the first 60 min with a mechanical load of 10 cmH2O. Thereafter ET-1 (10 nM), isoprenaline (0.5 nM), or the selective ETA antagonist BQ-610 (1 µM) or ETB antagonist BQ-788 (100 nM) (Bachem, Bubendorff, Switzerland) was applied to the buffer. After the 30-min period, ET-1 or isoprenaline concentration in the perfusion buffer was cumulatively increased every 30 min from 1 to 3, 10, 30, and 100 nM (ET-1) or from 0.1 to 1, 10, 100, and 1,000 nM (isoprenaline). Thus, to sum up, the groups in series 3 were as follows: dose response for ET-1 (n = 5); dose response for ET-1 in the presence of BQ-610 (n = 3); dose response for ET-1 in the presence of isoprenaline (n = 4); dose response for ET-1 in the presence of isoprenaline and BQ-610 (n = 6); dose response for ET-1 in the presence of BQ-788 (n = 5); dose response for isoprenaline (n = 5); dose response for isoprenaline in the presence of ET-1 (n = 5); dose response for isoprenaline in the presence of BQ-610 (n = 5); dose response for isoprenaline in the presence of ET-1 and BQ-610 (n = 6); and dose response for isoprenaline in the presence of ET-1 and BQ-788 (n = 7), BQ-610 (n = 4), BQ-788 (n = 4), and control (n = 3). The samples were stored at –20°C for use in the radioimmunoassays. The ventricles were stored at –70°C for the measurement of sCP mRNA by quantitative RT-PCR.

Radioimmunoassays. sCP in perfusion samples was determined by specific radioimmunoassay performed as described previously (67).

Determination of sCP mRNA by quantitative RT-PCR. Total RNA was extracted from ventricles using the acidic phenol method (7). The cDNA first strand was synthesized using M-MuLV RT. The quantitative PCR reactions were performed with an ABI 7700 SequenceDetection System using TaqMan chemistry, and the primers and probes for sCP and r18S RNA were described previously (42).

Statistical analysis. The results are given as means ± SE. The large data sets from the perfusion experiments were averaged in four time-point groups (0–5, 16–20, 26–30, and 36–40 min) in series 2 and in seven time-point groups (20–30, 50–60, 80–90, 110–120, 140–150, 170–180, and 200–210 min) in series 3, which were then compared. Two-way analysis of variance for repeated measures followed by the Student-Newman-Keuls post hoc test or Holm-Sidak post hoc test and parametric one-way analysis of variance for repeated measures followed by the Dunnett's test were used for the statistical analysis of the results (SigmaStat 3.11, Systat Software). Comparison between the control and the stimulated myocardium sample from the same animal was performed with the use of paired t-test. Differences at P < 0.05 were considered significant.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Effects of ET-1 and beta-adrenergic activation on salmon cardiac contractile function. Frank-Starling responses were determined to characterize the contractile function of the salmon ventricular muscle strip preparations (series 1). Stepwise increases of stretch resulted in well-developed Frank-Starling responses. The maximal force was observed with a stretch of 3 mm from the slack length of the preparation (7.5 ± 0.56 mm, n = 5, data not shown).

To find out the effects of ET-1 on salmon cardiac contractility, we added varying doses of ET-1 to the perfusion medium of the cardiac muscle preparations. ET-1 increased the contraction amplitude in a dose-dependent manner (Fig. 1A). The maximal response, 17 ± 1.3% compared with the basal level (P < 0.001), was attained with the highest dose tested (100 nM ET-1, Fig. 1A). An ~10% increase (P < 0.05) was observed with as little as 1 nM ET-1 (Fig. 1A). To test whether the inotropic effect is mediated by ETA receptors, similar experiments were performed in the presence of the selective ETA-receptor antagonist BQ-610 (125 nM). At this dose BQ-610 shifted the ET-1 on the contractility dose-response curve to the right and was able to completely abolish the effect of 1 nM ET-1 (Fig. 1A). As expected, isoprenaline increased markedly (47 ± 9.8%, P < 0.001) the contraction amplitude of salmon myocardial strip preparation (Fig. 1B).


Figure 1
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  		Fig. 1. A: dose-response relationship of endothelin-1 (ET-1) and contraction amplitude of salmon ventricular strip preparation (exposed to each dose level for 30 min, means ± SE). ETA-receptor antagonist (BQ-610, 125 nM) was added 30 min before the first ET-1 dose. B: dose-response relationship of isoprenaline (Iso) and contraction amplitude of salmon ventricular strip preparation (exposed to each dose level for 10 min; n = 6 strips, means ± SE). *P < 0.05; ***P < 0.001.

 
In a separate set of experiments with intact salmon ventricle preparation, we examined more specifically the effects of ET-1, the role of its A- and B-type receptors, and the possible interaction of the effects of ET-1 and isoprenaline (beta-adrenergic stimulation) on cardiac function. Contraction force was recorded concomitantly with the sampling of perfusate by measuring the pressure in the lumen of the ventricle. The maximal response, a 17 ± 4.7% increase in contraction amplitude compared with the basal level (P < 0.01), was attained with the concentration of 30 nM ET-1 (Fig. 2, A, B, and D). Isoprenaline (0.5 nM) treatment did not significantly potentiate the response induced by 10 nM ET-1 (25 ± 4.0% increase in contraction amplitude, P > 0.05 compared with ET-1 alone, Fig. 2A). ETA antagonist (BQ-610) was able to inhibit the response (P < 0.01, Fig. 2C). On the other hand, ETB-receptor antagonist (BQ-788) did not have any effect on the ET-1 response (Fig. 2D).


Figure 2
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  		Fig. 2. A–D: dose-response relationship of ET-1 and contraction amplitude of isolated salmon ventricle (exposed to each dose for 30 min, means ± SE). A: control, ET-1 alone, ET-1 in the presence of Iso, BQ-610 alone, and BQ-788 alone. B: ET-1 in the presence BQ-610. C: ET-1 in the presence of Iso and BQ-610. D: ET-1 in the presence of BQ-788. ETA antagonist (BQ-610, 1 µM), ETB antagonist (BQ-788, 100 nM), and Iso (0.5 nM) were added 30 min before the first ET dose. E–H: dose-response relationship of Iso and contraction amplitude of isolated salmon ventricle. E: control, Iso alone, and Iso in the presence of ET-1. F: Iso in the presence of BQ-610. G: Iso in the presence of ET-1 and Iso in the presence of ET-1 and BQ-610. H: Iso in the presence of ET-1 and BQ-788. ETA antagonist, ETB antagonist, and ET-1 (10 nM) were added 30 min before first Iso dose. NS, not significant. **P < 0.01.

 
The maximal response of isoprenaline (100 nM) was a 30 ± 13.1% increase in contraction amplitude compared with the control experiments (P < 0.05, Fig. 2, E and F). ET-1 or ET-receptor antagonists did not have any significant effect on the responses caused by isoprenaline (Fig. 2). ETA- or ETB-receptor antagonist alone had no significant effect on contraction amplitude (Fig. 2A), nor did ET-1 or isoprenaline have any significant effect on time parameters of isometric twitch compared with control experiments (Table 1, tested by ANOVA followed by Holm-Sidak post hoc test).


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  		Table 1. Effect of ET-1, Iso, BQ-610, BQ-788, ET together with Iso, and Iso together with ET on time parameters of salmon ventricle contraction

 
Effects of ET-1 and beta-adrenergic activation on sCP secretion from isolated perfused salmon ventricle. In series 2, we wanted to find out the effects of ET-1 on sCP release from isolated perfused salmon ventricle in basal conditions and during mechanical load. In the control experiments, sCP release declined steadily during the 40-min perfusion period to ~50% of the starting level (Fig. 3A). ET-1 (5 nM) stimulated sCP secretion and counteracted the decline (P < 0.01, Fig. 3B). Mechanical load (13 cmH2O) resulted in a 3.40 ± 0.081-fold increase of sCP release (P < 0.001, Fig. 3A). ET-1 did not affect the peak sCP release during mechanical load, but it kept the sCP secretion elevated compared with control after the load was released (Fig. 3C). The ETA antagonist BQ-610 inhibited significantly the stimulatory effect of mechanical load on sCP release (P < 0.01; Fig. 3D).


Figure 3
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  		Fig. 3. Release of salmon cardiac peptide (sCP) from isolated perfused salmon ventricle in response to A: mechanical load of 13 cmH2O; B: 5 nM ET-1; C: mechanical load of 13 cmH2O in the presence of 5 nM ET-1; D: mechanical load of 13 cmH2O in the presence of 125 nM ETA antagonist BQ-610 (means ± SE). n, Number of isolated salmon ventricle preparations tested. **P < 0.01; ***P < 0.001.

 
In series 3, we examined which endothelin receptor subtype (ETA or ETB) is responsible for the effect of ET-1 and whether there is any interaction between the cardiac effects of ET-1 and beta-adrenergic stimulation. In keeping with our results described above, in the control experiments sCP release declined steadily during the 210-min perfusion period to ~30% of the starting level (Figs. 4 and 5). This decline was counteracted by 10–100 nM ET-1. ET-1 (10 nM) increased the release of sCP 3.3 ± 0.14 times over the control (P < 0.05, Figs. 4, A, B, and D). The ETA antagonist BQ-610 did not block the effects of ET-1 (Fig. 4B). On the other hand, the ETB antagonist BQ-788 (100 nM) enhanced the effect of ET-1 (P < 0.01, Fig. 4D). Isoprenaline (0.1–1,000 nM) did not affect sCP secretion when tested alone (Fig. 5, A and B). However, isoprenaline (0.1 nM) caused a marked increase of sCP release (5.4 ± 0.07 times increase over the control) in the presence of 10 nM ET-1 (P < 0.01 compared with isoprenaline alone, Fig. 5, A, C, and D), which was partly blocked by the ETA antagonist BQ-610 but not the ETB antagonist BQ-788 (P < 0.05, Fig. 5, C and D). BQ-610 alone did not affect sCP release (Fig. 4A). BQ-788, however, markedly stimulated the basal sCP release compared with control experiments (P < 0.05, Fig. 4A).


Figure 4
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  		Fig. 4. Effects of ET-1 on sCP secretion from isolated salmon ventricle (exposed to each dose for 30 min, means ± SE). A: control, ET-1 alone, ET-1 in the presence of Iso, BQ-610 alone, and BQ-788 alone. B: ET-1 in the presence BQ-610. C: ET-1 in the presence of Iso and BQ-610. D: ET-1 in the presence of BQ-788. ETA antagonist (BQ-610, 1 µM), ETB antagonist (BQ-788, 100 nM), and Iso (0.5 nM) were added 30 min before first ET-1 dose. n, Number of isolated salmon ventricle preparations tested. *P < 0.05; **P < 0.01.

 

Figure 5
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  		Fig. 5. Effects of Iso on sCP secretion from isolated salmon ventricle (exposed to each dose for 30 min, means ± SE). A: control, Iso alone, and Iso in the presence of ET-1. B: Iso in the presence of BQ-610. C: Iso in the presence of ET-1 and Iso in the presence of ET-1 and BQ-610. D: Iso in the presence of ET-1 and BQ-788. ETA antagonist (BQ-610, 1 µM), ETB antagonist (BQ-788, 100 nM), and ET-1 (10 nM) were added 30 min before first Iso dose. n, Number of isolated salmon ventricle preparations tested. *P < 0.05; **P < 0.01.

 
Effect of ET-1 on sCP mRNA levels. Because of the stimulatory effects of ET-1 on sCP release and the known efficacy of ET-1 in inducing mammalian brain natriuretic peptide (BNP) gene expression, we were interested to find out whether ET-1 affects salmon cardiac sCP gene expression. Three-hour treatment with cumulatively increasing doses of human ET-1 (1–100 nM) failed to have any effect on salmon ventricular sCP mRNA levels, as tested by real-time quantitative RT-PCR (data not shown).


   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Our previous results have shown that mechanical load is a major stimulus for the secretion of the novel cardiac natriuretic peptide (sCP) (36, 42, 65–67, 72). In this study we wanted to characterize the effects of ET-1 on the contractile and endocrine function of the salmon heart. In addition, we wanted to investigate the interactions between two important regulators of heart function, ET-1 and beta-adrenergic stimulation, both of which are activated in various pathophysiological conditions. Cardiovascular effects of mammalian ET-1 and the trout ET-2-like peptide have been studied previously (23, 40, 50, 74), but the endocrine and inotropic effects of ET-1 on fish heart are not known. The present study provides the first evidence for an important direct role of ET-1 as a cardiac secretagogue and inotropic agent in fish. It also reveals interesting synergism between the cardiac effects of ET-1 and beta-adrenergic stimulation.

The main findings of the present study were as follows: 1) ET-1 has a positive inotropic effect on salmon myocardium, 2) ET-1 stimulates the secretion but does not affect the mRNA levels of salmon cardiac peptide, 3) ET-1 and beta-adrenergic stimulation have a synergistic effect at least on the endocrine function of salmon heart, 4) both the endocrine and contractile effects of ET-1 appear to be mainly mediated by ETA receptors, and 5) ETB receptors seem to have an opposite role to ETA receptors in the regulation of salmon cardiac endocrine function.

Effects of ET-1 and beta-adrenergic activation on salmon cardiac contractile function. An important difference between the control of cardiac output in fish and mammals is the much larger role of variation in the stroke volume in fish. A two- or threefold increase in stroke volume is possible in fish, and the control of stroke volume and contractility (inotropy) has a predominant role in the regulation of the cardiac output (16), as opposed to the major role of chronotropic regulation in mammalian heart. Cardiac contractility is modulated neurally, humorally, and locally. beta-Adrenergic stimulation has a positive inotropic effect in salmonids (1, 16). Therefore, in our studies, isoprenaline served as a positive control for inotropic effect in salmon heart. Isoprenaline (10 µM) increased the contraction amplitude of salmon ventricle of ~1.5 times compared with control.

ET-1 was found to have a positive inotropic effect, suggesting that it has a role in the regulation of the contractile function of the salmon heart. The maximal increase in the contraction amplitude was, however, less than that produced by isoprenaline. Although the maximal response in salmon (17% increase in contraction amplitude) was attained with 30 nM (intact ventricle) or 100 nM (myocardial strip) ET-1, a dose as low as 1 nM ET-1 was able to produce about 11–13% increase in the contraction amplitude. Based on previous literature, the ratio of potency of ET-1 over that of isoprenaline appears to be highly variable depending on the animal species studied. ET-1 has been found to elicit the most pronounced positive inotropic effect on the rabbit papillary muscle (62). This effect was induced at 1 nM, reaching maximum at 30 nM ET-1 (62). The maximum response amounted to 55% of that of isoprenaline (62). In the rat, however, the effect of ET-1 reached the maximum at 3 nM, and the maximum response to ET-1 amounted to <20% of that to isoprenaline (62). Our results show that, in salmon, the maximum response to ET-1 is 36% of that of isoprenaline. Therefore, ET-1 seems to be a fairly potent inotropic agent in fish.

Our results indicate that ETA receptors mediate the inotropic effect of ET-1 in salmon, as is the case in humans (51). The dose-response curve of the positive inotropic effect of ET-1 on salmon myocardium was shifted to the right with a selective antagonist of the ETA receptor, a finding that is consistent with competitive inhibition. The inability of 1 µM BQ-610 to completely inhibit the inotropic effect of large doses of ET-1 is probably dose related. ET-1 concentration of 100 nM appears to be supramaximal (see Fig. 2A), and, therefore, it may have other unknown effects in cardiac tissue. The concentration of maximum 1 µM BQ-610 was selected on the basis of mammalian studies (12, 13, 28). Furthermore, the solubility of BQ-610 makes it very difficult to use higher concentrations. BQ-610 (1 µM) itself did not cause any significant cardiac effects, as shown in Fig. 2A. As the structure of fish ETA receptor is not known, we cannot rule out the possibility that a structural difference in fish ETA receptor, compared with its mammalian homologue, may yield the fish receptor less sensitive to BQ-610 inhibition.

The selective ETB receptor antagonist BQ-788 did not affect the cardiac contractile effects of ET-1 in the salmon. The result is consistent with a recent study with Atlantic cod in which the ETB agonist BQ-3020 did not cause any significant change in cardiac output (60). In rat heart, however, ETB receptor-mediated inotropic effects of ET-1 have been reported (4). Results in mouse have indicated opposite roles for ETA and ETB-receptors in the regulation of contractile force (52). ETA-receptor activation accounts for ET-1-mediated enhancement of contractile force during elevated load, whereas ETB receptor activation has an inhibitory action on contractile function (52). Activation of endothelial cell ETB receptors can produce vasodilatation by releasing vasorelaxing factors, such as nitric oxide (NO) (71). It has been shown that the positive inotropic effect of ET-1 in rat heart is augmented with inhibition of NO synthase (34). Therefore, ETB receptor activation-induced NO release may play an inhibitory role in the regulation of contractile force during loading. Another possible mechanism for the ETB blockade-induced augmentation of contractility would be the decreased clearance of locally acting ET-1, thus indicating an increase in ET-1 binding to ETA receptors (52).

The results of the present study showed that ET-1 does not affect the contraction time parameters, in agreement with earlier studies in mammals (27, 51). The subcellular mechanism that is responsible for the positive inotropic effect of ET-1 in mammals includes a considerable increase in myofibrillar sensitivity to Ca2+ and a moderate increase in the intracellular Ca2+ transient (48, 61). The cellular mechanisms for the inotropic effect of ET-1 in salmon myocardium are not known. In mammals, stimulation of the ETA or ETB receptors activates the phosphoinositol pathway via phospholipase C-beta, causing the activation of protein kinase C and the release of inositol 1,4,5-trisphosphate and a rise in the intracellular Ca2+ concentration (10).

In rainbow trout, isoprenaline has been shown to cause a shortening of the time to peak force and an increase in relaxation time parameters (9). We did not find any effects on the time parameters of isometric twitch. A partial explanation for the discrepancy may be due to difficulties in defining the exact start and end points of contraction. In mammals, isoprenaline increases the activity of protein kinase A and enhances Ca2+ uptake into the sarcoplasmic reticulum and therefore induces a shortening of the time to peak force and an acceleration of the relaxation (58). Stimulation of beta-adrenergic receptors activates adenylate cyclase via Gs, initiating the protein kinase A-dependent phosphorylation of ion channels and regulatory proteins, such as L-type Ca2+ channels, phospholamban, and myofibrillar proteins involved in the cardiac excitation-contraction coupling and energy metabolism (15).

Effects of ET-1 and beta-adrenergic activation on salmon cardiac peptide secretion. ET-1 is a major ANP and BNP secretagogue in mammals (5, 6, 18, 24). In the present study, we found that ET-1 stimulates cardiac natriuretic peptide (sCP) secretion from salmon ventricle but does not augment the sCP release induced by 13 cmH2O mechanical load, a stimulus previously found to cause a marked and consistent increase of sCP release (36). This was unexpected because we have earlier found that ET-1 markedly potentiates load-induced cardiac natriuretic peptide release in vivo and in vitro in the rat (41, 43). Moreover, passive immunization with an antiserum against ET-1 has been found to reduce both the basal and volume load-induced levels of plasma ANP in rats (20). With the consideration of our endothelin receptor antagonist data (see below), a likely explanation for the discrepant result is that the stimulus used (13 cmH2O) was a near-maximal one and that ET-1 is able to shift the dose-response curve of mechanical load versus natriuretic peptide release to the left but does not affect the maximal response. This conclusion is supported by our finding that an increase of sCP release was indeed observed in the presence of ET-1, but only after the 13 cmH2O load was released (see Fig. 3C).

We found in the present study that an ETA-receptor antagonist was able to inhibit the ET-1-induced release of sCP. We have previously found that the antagonism of ETA/ETB receptors by bosentan decreases, and the combined blockage of ETA/ETB and angiotensin II receptor type 1 almost completely abolishes the response of ANP secretion to volume load in the rat (41). The proximity of ET-1-producing endothelial cells and cardiomyocytes and the presence of endothelin receptors on the cardiomyocytes (11) suggest that ET-1 regulates ANP secretion, possibly by modulation of Ca2+ (70). ET-1 has been proposed to have a permissive role, facilitating the release of ANP from cardiac myocytes. It may act as a tonic regulator of intracellular Ca2+, which, if interrupted by an endothelin antagonist, may render the ANP-secreting myocytes less sensitive to stretch (20). It has been reported that enhanced Ca2+ influx plays a significant role in ET-1-stimulated ANP secretion but that the release of intracellular Ca2+ from the sarcoplasmic reticulum does not participate in the secretory response (56). In the present study, an ETA antagonist markedly attenuated the load-induced secretion of sCP. Thus, ET-1, via ETA receptors, appears to have an important physiological role as a mediator of volume load-induced sCP secretion from salmon ventricle. Finding out whether other endogenous paracrine/autocrine factors, such as angiotensin II, have similar activity requires further study.

Both {alpha}- and beta-adrenergic agonists have been found to stimulate ANP secretion in isolated rat atria (55). The secretory response pattern of norepinephrine reflects a predominance of beta-adrenergic activity (55). In superfused rabbit atria, the isoproterenol-stimulated ANP release appears to be mediated by cAMP and does not require extracellular calcium (2). Our present studies showed that beta-adrenergic activation alone does not stimulate salmon cardiac peptide secretion. It does however, have a strong synergistic effect with ET-1 on sCP release. These findings indicate that there is a synergism between the cellular signaling pathways of ET-1 and beta-adrenergic stimulation. The mechanism for the synergism is not known, but it may involve the concurrent activation of two separate but interconnected signaling pathways. The effects of both are mediated by G protein-coupled receptors, Gq-activating phospholipase C in the case of ET-1, and Gs-activating adenylate cyclase-PKA pathway in the case of beta-adrenergic stimulation. Similar synergism has previously been described with corticotropin-releasing hormone and arginine vasotocin stimulating the release of ACTH (3). In addition, it has been found that ET-1 alone does not affect the contractile function of canine ventricular myocardium, but clear effects on contractility can be observed in the presence of norepinephrine (8). This effect again required the simultaneous activation of protein kinase A and protein kinase C signaling pathways (8). Furthermore, it has been shown that although ET-1 alone does not affect intracellular cAMP concentrations, it enhances isoprenaline-stimulated cAMP accumulation (76). It thus seems that ET-1 and beta-adrenergic activation are engaged in cross talk at different levels of their respective signaling pathways (8). For instance, a positive feedback mechanism seems to exist at the level of the synthesis of norepinephrine by which ET-1 increases the blood concentration of norepinephrine (46). In addition, norepinephrine facilitates the expression of mRNA that encodes the prepro-ET-1 (45) and the production of ET-1 (77).

Our results showed that the inhibition of ETB receptors with a selective antagonist increased the release of sCP. A possible mechanism for the ETB inhibition-induced stimulation would be the decreased clearance of ET-1, thus inducing an increase in ET-1 binding to ETA receptors. Especially in the lungs, ETB receptors have been implicated in the clearance of ET- 1 from plasma (19).

Effects of ET-1 on salmon cardiac peptide gene expression. Our present results show that ET-1 does not affect sCP gene expression, at least in the short term. We have previously demonstrated that mechanical load, which is an extremely potent stimulator of the secretion of sCP, is similarly inert with regard to gene expression (36). Our findings, therefore, resemble those obtained with mammalian ANP. ET-induced secretion of ANP by an isolated rat atrial preparation is not associated with acute changes in ANP mRNA levels (5), nor are ANP mRNA levels affected by 8-h stretch (5). In contrast to ANP, stretch (44) and ET-1 (6) induce a marked increase in BNP gene expression in isolated rat atria. Short stimulation (60-min atrial stretching) is able to induce an increase in BNP gene expression (44). Despite the fact that the peptide and gene of sCP contain features of both ANP and BNP (42), functional studies (36, 65, 72) and comparative structural analyses (63, 64, 69) place it clearly in the group of ANP-type peptides.


   ACKNOWLEDGMENTS
 
We gratefully acknowledge the staff of Game and Fisheries Institute in Taivalkoski, Muonio, and Laukaa, and the staff of the hatchery of Imatran Voima power plant in Muhos for providing the salmon used in this study. We are grateful to Eero Kouvalainen for help with statistical analyses. We thank Helka Koisti, Anneli Rautio, Tuula Taskinen, and Alpo Vanhala for expert technical assistance. This study was supported by grants from the Sigrid Juselius Foundation, the Academy of Finland, the Finnish Foundation for Cardiovascular Research, the Kemira Foundation, and the University of Oulu Foundation.


   FOOTNOTES
 

Address for reprint requests and other correspondence: O. Vuolteenaho, Dept. of Physiology, POB 5000, FIN-90014, Univ. of Oulu, Oulu, Finland (E-mail: olli.vuolteenaho{at}oulu.fi)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Ask JA, Stene-Larsen G, and Helle KB. Temperature effects on the beta2-adrenoceptors of the trout atrium. J Comp Physiol [B] 143: 161–168, 1981.
  2. Azizi C, Carayon A, Masson F, Noe E, Barthelemy C, Eurin J, Maistre G, and Legrand JC. Mechanisms of isoproterenol-induced atrial natriuretic peptide release from superfused rabbit atria. Am J Physiol Heart Circ Physiol 265: H1283–H1288, 1993.[Abstract/Free Full Text]
  3. Baker BI, Bird DJ, and Buckingham JC. In the trout, CRH and AVT synergize to stimulate ACTH release. Regul Pept 67: 207–210, 1996.[CrossRef][Web of Science][Medline]
  4. Beyer ME, Slesak G, and Hoffmeister HM. In vivo hemodynamic and inotropic effects of the endothelinB agonist IRL 1620. J Cardiovasc Pharmacol 26: S190–S192, 1995.
  5. Bruneau BG and De Bold AJ. Selective changes in natriuretic peptide and early response gene expression in isolated rat atria following stimulation by stretch or endothelin-1. Cardiovasc Res 28: 1519–1525, 1994.[Web of Science][Medline]
  6. Bruneau BG, Piazza LA, and De Bold AJ. BNP gene expression is specifically modulated by stretch and ET-1 in a new model of isolated rat atria. Am J Physiol Heart Circ Physiol 273: H2678–H2686, 1997.[Abstract/Free Full Text]
  7. Chomczynski P and Sacchi N. Single-step method of RNA isolation by acid guanidium thiocyanate-phenol-chloroform extraction. Anal Biochem 162: 156–159, 1987.[Web of Science][Medline]
  8. Chu L, Takahashi R, Norota I, Miyamoto T, Takeishi Y, Ishii K, Kubota I, and Endoh M. Signal transduction and Ca2+ signaling in contractile regulation induced by crosstalk between endothelin-1 and norepinephrine in dog ventricular myocardium. Circ Res 92: 1024–1032, 2003.[Abstract/Free Full Text]
  9. Coyne MD, Kim CS, Cameron JS, and Gwathmey JK. Effects of temperature and calcium availability on ventricular myocardium from rainbow trout. Am J Physiol Regul Integr Comp Physiol 278: R1535–R1544, 2000.[Abstract/Free Full Text]
  10. Cramer H, Muller-Esterl W, and Schroeder C. Subtype-specific endothelin-A and endothelin-B receptor desensitization correlates with differential receptor phosphorylation. J Cardiovasc Pharmacol 31: S203–S206, 1998.
  11. Davenport AP, Nunez DJ, Kaufmann AJ, and Brown MJ. Autoradiographical localization of binding sites for porcine 125I endothelin-1 in human, pigs, and rats: fuctional relevance in humans. J Cardiovasc Pharmacol 13: S166–S170, 1989.
  12. Deng LY, Li JS, and Schiffrin EL. Endothelin receptor subtypes in resistance arteries from humans and rats. Cardiovasc Res 29: 532–535, 1995.[CrossRef][Web of Science][Medline]
  13. Ding KH, Zhong Q, and Isales CM. Glucose-dependent insulinotropic peptide stimulates thymidine incorporation in endothelial cells: role of endothelin-1. Am J Physiol Endocrinol Metab 285: E390–E396, 2003.[Abstract/Free Full Text]
  14. Donckier J, Hanet C, Galanti L, Stoleru L, and Van Mechelen H. Low-dose endothelin-1 potentiates volume-induced secretion of atrial natriuretic factor. Am J Physiol Heart Circ Physiol 263: H939–H944, 1992.[Abstract/Free Full Text]
  15. Dzimiri N. Receptor crosstalk: implications for cardiovascular function, disease and therapy. Eur J Biochem 269: 4713–4730, 2002.[Web of Science][Medline]
  16. Farrell AP. Cardiovascular system. In: The Physiology of Fishes, edited by Evans DH. Boca Raton, FL: CRC, 1993.
  17. Farrell AP, Johansen JA, and Graham MS. The role of the pericardium in the cardiac performance of the trout (Salmo gairdneri). Physiol Zool 61: 213–221, 1988.
  18. Fukuda Y, Hirata Y, Yoshimi H, Kojima T, Kobayashi Y, Yanagisawa M, and Masaki T. Endothelin is a potent secretagogue for atrial natriuretic peptide in cultured rat atrial myocytes. Biochem Biophys Res Commun 155: 167–172, 1988.[CrossRef][Web of Science][Medline]
  19. Fukuroda T, Fujikawa T, Ozaki S, Ishikawa K, Yano M, and Nishikibe M. Clearance of circulating endothelin-1 by ETB receptors in rats. Biochem Biophys Res Commun 199: 1461–1465, 1994.[CrossRef][Web of Science][Medline]
  20. Fyhrquist F, Sirviö ML, Helin K, Saijonmaa O, Metsärinne K, Paakkari I, Järvinen A, and Tikkanen I. Endothelin antiserum decreases volume-stimulated and basal plasma concentration of atrial natriuretic peptide. Circulation 88: 1172–1176, 1993.[Abstract/Free Full Text]
  21. Gingerich WH and Drottar KR. Plasma catecholamine concentrations in rainbow trout (Salmo gairdneri) at rest and after anesthesia and surgery. Gen Comp Endocrinol 73: 390–397, 1989.[CrossRef][Web of Science][Medline]
  22. Haynes WG and Webb DJ. Contribution of endogenous generation of endothelin-1 to basal vascular tone. Lancet 344: 852–854, 1994.[CrossRef][Web of Science][Medline]
  23. Hoagland TM, Weaver L, Conlon JM, Wang Y, and Olson KR. Effects of endothelin-1 and homologous trout endothelin on cardiovascular function in rainbow trout. Am J Physiol Regul Integr Comp Physiol 278: R460–R468, 2000.[Abstract/Free Full Text]
  24. Hu JR, Berninger UG, and Lang RE. Endothelin stimulates atrial natriuretic peptide (ANP) release from rat atria. Eur J Pharmacol 158: 177–178, 1988.[CrossRef][Web of Science][Medline]
  25. Inoue K, Naruse K, Yamagami S, Mitani H, Suzuki N, and Takei Y. Four functionally distinct C-type natriuretic peptides found in fish reveal evolutionary history of the natriuretic peptide system. Proc Natl Acad Sci USA 19: 10079–10084, 2003.
  26. Inoue K, Sakamoto T, Yuge S, Iwatani H, Yamagami S, Tsutsumi M, Hori H, Cerra MC, Tota B, Suzuki N, Okamoto N, and Takei Y. Structural and functional evolution of three cardiac natriuretic peptides. Mol Biol Evol 22: 2428–2434, 2005.[Abstract/Free Full Text]
  27. Ishikawa T, Yanakisawa M, Kimura S, Goto K, and Masaki T. Positive inotropic action of novel vasoconstrictor peptide endothelin on guinea pig atria. Am J Physiol Heart Circ Physiol 255: H970–H973, 1988.[Abstract/Free Full Text]
  28. Kanyicska B, Lerant A, and Freeman ME. Endothelin is an autocrine regulator of prolactin secretion. Endocrinology 139: 5164–5173, 1998.[Abstract/Free Full Text]
  29. Kawakoshi A, Hyodo S, Inoue K, Kobayashi Y, and Takei Y. Four natriuretic peptides (ANP, BNP, VNP and CNP) coexist in the sturgeon: identification of BNP in fish lineage. J Mol Endocrinol 32: 547–555, 2004.[Abstract]
  30. Kawakoshi A, Hyodo S, Yasuda A, and Takei Y. A single and novel natriuretic peptide is expressed in the heart and brain of the most primitive vertebrate, the hagfish (Eptatretus burgeri). J Mol Endocrinol 31: 209–220, 2003.[Abstract]
  31. Kedzierski RM and Yanagisawa M. Endothelin system: the double-edged sword in health and disease. Annu Rev Pharmacol Toxicol 41: 851–876, 2001.[CrossRef][Web of Science][Medline]
  32. Kelly RA, Eid H, Krämer BK, O'Neill M, Liang BT, Reers M, and Smith TW. Endothelin enhances the contractile responsiveness of adult rat ventricular myocytes to calcium by a pertussis toxin-sensitive pathway. J Clin Invest 86: 1164–1171, 1990.[Web of Science][Medline]
  33. Kelso EJ, McDermott BJ, Silke B, and Spiers JP. Endothelin A receptor subtype mediates endothelin-induced contractility in left ventricular cardiomyocytes isolated from rabbit myocardium. J Pharmacol Exp Ther 294: 1047–1052, 2000.[Abstract/Free Full Text]
  34. Kinnunen P, Szokodi I, Nicholls MG, and Ruskoaho H. Impact of NO on ET-1- and AM-induced inotropic responses: potentiation by combined administration. Am J Physiol Regul Integr Comp Physiol 279: R569–R575, 2000.[Abstract/Free Full Text]
  35. Kiss O, Zima E, Soos P, Kekesi V, Juhasz-Nagy A, and Merkely B. Intracoronary endothelin-1 infusion combined with systemic isoproterenol treatment: antagonistic arrhythmogenic effects. Life Sci 18: 537–548, 2004.[CrossRef]
  36. Kokkonen K, Vierimaa H, Bergström S, Tervonen V, Arjamaa O, Ruskoaho H, Järvilehto M, and Vuolteenaho O. Novel salmon cardiac peptide hormone is released from the ventricle by regulated secretory pathway. Am J Physiol Endocrinol Metab 278: E285–E292, 2000.[Abstract/Free Full Text]
  37. Krämer BK, Ackermann M, Kohler SM, and Riegger GAJ. Role of endothelin in hypertension. Clin Investig 72: 88–93, 1994.[Web of Science][Medline]
  38. Krämer BK, Nishida M, Kelly RA, and Smith TW. Endothelins. Myocardial actions of a new class of cytokines. Circulation 85: 350–356, 1992.[Abstract/Free Full Text]
  39. Krämer BK, Smith TW, and Kelly RA. Endothelin and increased contractility in adult rat ventricular myocytes. Role of intracellular alkalosis induced by activation of the protein kinase C-dependent Na+-H+ exchanger. Circ Res 68: 269–279, 1991.[Abstract/Free Full Text]
  40. Le Mével JC, Delarue C, Mabin D, and Vaudry H. Central and peripheral administration of endothelin-1 induces an increase in blood pressure in conscious trout. Am J Physiol Regul Integr Comp Physiol 276: R1010–R1017, 1999.[Abstract/Free Full Text]
  41. Leskinen H, Vuolteenaho O, and Ruskoaho H. Combined inhibition of endothelin and angiotensin II receptors block volume load induced cardiac hormone release. Circ Res 80: 114–123, 1997.[Abstract/Free Full Text]
  42. Majalahti-Palviainen T, Hirvinen M, Tervonen V, Ilves M, Ruskoaho H, and Vuolteenaho O. Gene structure of a new cardiac peptide hormone: a model for heart-specific gene expression. Endocrinology 141: 731–740, 2000.[Abstract/Free Full Text]
  43. Mäntymaa P, Leppäluoto J, and Ruskoaho H. Endothelin stimulates basal and stretch-induced atrial natriuretic peptide secretion from the perfused rat heart. Endocrinology 126: 587–595, 1990.[Abstract/Free Full Text]
  44. Mäntymaa P, Vuolteenaho O, Marttila M, and Ruskoaho H. Atrial stretch induces rapid increase in brain natriuretic peptide but not in atrial natriuretic peptide gene expression in vitro. Endocrinology 133: 1470–1473, 1993.[Abstract/Free Full Text]
  45. Masaki T, Kimura S, Yanagisawa M, and Goto K. Molecular and cellular mechanism of endothelin regulation. Implications for vascular function. Circulation 84: 1457–1468, 1991.[Free Full Text]
  46. Miller WL, Redfield MM, and Burnett JC Jr. Integrated cardiac, renal, and endocrine actions of endothelin. J Clin Invest 83: 317–320, 1989.[Web of Science][Medline]
  47. Molenaar P, O'Reilly G, Sharkey A, Kuc RE, Harding DP, Plumpton C, Gresham GA, and Davenport AP. Characterization and localization of endothelin receptor subtypes in the human atrioventricular conducting system and myocardium. Circ Res 72: 526–538, 1993.[Abstract/Free Full Text]
  48. Moravec CS, Reynolds EE, Stewart RW, and Bond M. Endothelin is a positive inotropic agent in human and rat heart in vitro. Biochem Biophys Res Commun 159: 14–18, 1989.[CrossRef][Web of Science][Medline]
  49. Neubauer S, Ertl G, Haas U, Pulzer F, and Kochsiek K. Effects of endothelin-1 in isolated perfused rat heart. J Cardiovasc Pharmacol 16: 1–8, 1990.[Web of Science][Medline]
  50. Olson KR, Duff DG, Farrell AP, Keen J, Kellogg MD, Kullman D, and Villa J. Cardiovascular effects of endothelin in trout. Am J Physiol Heart Circ Physiol 260: H1214–H1223, 1991.[Abstract/Free Full Text]
  51. Pieske B, Beyermann B, Breu V, Löffler BM, Schlotthauer K, Maier LS, Schmidt-Schweda S, Just H, and Hasefuss G. Functional effects of endothelin end regulation of endothelin receptors in isolated human nonfailing and failing myocardium. Circulation 99: 1802–1809, 1999.[Abstract/Free Full Text]
  52. Piuhola J, Mäkinen M, Szokodi I, and Ruskoaho H. Dual role of endothelin-1 via ETA and ETB receptors in regulation of cardiac contractile function in mice. Am J Physiol Heart Circ Physiol 285: H112–H118, 2003.[Abstract/Free Full Text]
  53. Rubanyi GM and Botelho LH. Endothelins. FASEB J 5: 2713–2720, 1991.[Abstract]
  54. Saetrum Opgaard O, Möller S, De Vries R, Edvinsson L, and Saxena P. Positive inotropic responses mediated by endothelin ETA and ETB receptors in human myocardial trabeculae. Clin Sci (Lond) 99: 161–168, 2000.[Medline]
  55. Schiebinger RJ, Baker MZ, and Linden J. Effect of adrenergic and muscarinic cholinergic agonists on atrial natriuretic peptide secretion by isolated rat atria. Potential role of the autonomic nervous system in modulating atrial natriuretic peptide secretion. J Clin Invest 80: 1687–1691, 1987.[Web of Science][Medline]
  56. Schiebinger R and Gomez-Sanchez C. Endothelin: a potent stimulus of atrial natriuretic peptide secretion by superfused rat atria and its dependency on calcium. Endocrinology 127: 119–125, 1990.[Abstract/Free Full Text]
  57. Schiebinger R and Greening KM. Interaction between stretch and hormonally stimulated atrial natriuretic peptide secretion. Am J Physiol Heart Circ Physiol 262: H78–H83, 1992.[Abstract/Free Full Text]
  58. Scholz H. Effects of beta- and alpha-adrenoceptor activators and adrenergic transmitter releasing agents on the mechanical activity of the heart. In: Adrenergic Activators and Inhibitors. Part I. Handbook of Experimental Pharmacology, edited by Szekeres L. Springer-Verlag Berlin Heidelberg, vol. 54/I, 1980.
  59. Skovrak JP, Nazian SJ, and Dietz JR. Endothelin acts as a paracrine regulator of stretch induced atrial natriuretic peptide release. Am J Physiol Regul Integr Comp Physiol 269: R1093–R1098, 1995.[Abstract/Free Full Text]
  60. Stenslokken KO, Sundin L, and Nilsson GE. Endothelin receptors in teleost fishes: cardiovascular effects and branchial distribution. Am J Physiol Regul Integr Comp Physiol 290: R852–R860, 2006.[Abstract/Free Full Text]
  61. Takanashi M and Endoh M. Concentration- and time-dependence of phosphoinositide hydrolysis induced by endothelin-1 in relation to the positive inotropic effect in the rabbit ventricular myocardium. J Pharmacol Exp Ther 262: 1189–1194, 1992.[Abstract/Free Full Text]
  62. Takanashi M and Endoh M. Characterization of positive inotropic effect of endothelin on mammalian ventricular myocardium. Am J Physiol Heart Circ Physiol 261: H611–H619, 1991.[Abstract/Free Full Text]
  63. Takei Y. Does the natriuretic peptide system exist throughout the animal and plant kingdom? Comp Biochem Physiol B Biochem Mol Biol 129: 559–573, 2001.[CrossRef][Medline]
  64. Takei Y and Hirose S. The natriuretic peptide system in eels: a key endocrine system for euryhalinity? Am J Physiol Regul Integr Comp Physiol 282: R940–R951, 2002.[Abstract/Free Full Text]
  65. Tervonen V, Arjamaa O, Kokkonen K, Ruskoaho H, and Vuolteenaho O. A novel cardiac hormone related to A-, B- and C-type natriuretic peptides. Endocrinology 139: 4021–4025, 1998.[Abstract/Free Full Text]
  66. Tervonen V, Ruskoaho H, Lecklin T, Ilves M, and Vuolteenaho O. Salmon cardiac natriuretic peptide is a volume-regulating hormone. Am J Physiol Endocrinol Metab 283: E353–E361, 2002.[Abstract/Free Full Text]
  67. Tervonen V, Ruskoaho H, and Vuolteenaho O. Novel cardiac peptide hormone in several teleosts. J Endocrinol 166: 407–418, 2000.[Abstract]
  68. Thomas GP, Sims SM, and Karmazyn M. Differential effects of endothelin-1 on basal and isoprenaline-enhanced Ca2+ current in guinea-pig ventricular myocytes. J Physiol 15: 55–65, 1997.
  69. Toop T and Donald JA. Comparative aspects of natriuretic peptide physiology in non-mammalian vertebrates: a review. J Comp Physiol [B] 174: 189–204, 2004.[CrossRef][Medline]
  70. Uusimaa PA, Hassinen IE, Vuolteenaho O, and Ruskoaho H. Endothelin-induced atrial natriuretic peptide release from cultured neonatal cardiac myocytes: the role of extracellular calcium and protein kinase-C. Endocrinology 130: 2455–2464, 1992.[Abstract/Free Full Text]
  71. Verhaar MC, Strachan FE, Newby DE, Cruden NL, Koomans HA, Rabelink TJ, and Webb DJ. Endothelin-A receptor antagonist-mediated vasodilatation is attenuated by inhibition of nitric oxide synthesis and by endothelin-B receptor blockade. Circulation 97: 752–756, 1998.[Abstract/Free Full Text]
  72. Vierimaa H, Hirvinen M, Tervonen V, Arjamaa O, Ruskoaho H, and Vuolteenaho O. Pronatriuretic peptide is a sensitive marker of the endocrine function of teleost heart. Am J Physiol Endocrinol Metab 282: E843–E850, 2002.[Abstract/Free Full Text]
  73. Wang J and Morgan JP. Endothelin reverses the effects of acidosis on the intracellular Ca2+ transients and contractility in ferret myocardium. Circ Res 71: 631–639, 1992.[Abstract/Free Full Text]
  74. Wang Y, Olson KR, Smith MP, Russell MJ, and Conlon JM. Purification, structural characterization, and myotropic activity of endothelin from trout, Oncorhynchus mykiss. Am J Physiol Regul Integr Comp Physiol 277: R1605–R1611, 1999.[Abstract/Free Full Text]
  75. Watanabe T and Endoh M. Antiadrenergic effects of endothelin-1 on the L-type Ca2+ current in dog ventricular myocytes. J Cardiovasc Pharmacol 36: 344–350, 2000.[CrossRef][Web of Science][Medline]
  76. Wu-Wong JR and Opgenorth TJ. Endothelin and isoproterenol counter-regulate cAMP and mitogen-activated protein kinases. J Cardiovasc Pharmacol 31: S185–S191, 1998.
  77. Yanagisawa M, Kurihara H, Kimura S, Tomobe Y, Kobayashi M, Mitsui Y, Yzaki Y, Goto K, and Masaki T. A novel potent vasoconstrictor peptide produced by vascular endothelial cells. Nature 332: 411–415, 1988.[CrossRef][Medline]




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