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Am J Physiol Heart Circ Physiol 289: H1702-H1709, 2005. First published June 10, 2005; doi:10.1152/ajpheart.00892.2004
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Positive inotropic and negative lusitropic effects of endothelin receptor agonism in vivo

D. Konrad,1 A. Oldner,1 M. Wanecek,1 A. Rudehill,1 E. Weitzberg,1 B. Biber,2 G. Johansson,2 S. Häggmark,2 and M. Haney2

1Department of Surgical Sciences, Section for Anaesthesiology and Intensive Care, Karolinska Institute, Stockholm; and 2Perioperative and Surgical Sciences, Anesthesiology and Intensive Care Medicine, Umeå University, Umeå, Sweden

Submitted 30 August 2004 ; accepted in final form 31 May 2005


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
The endothelin (ET) system is involved in the regulation of myocardial function in health as well as in several diseases, such as congestive heart failure, myocardial infarction, and septic myocardial depression. Conflicting results have been reported regarding the acute contractile properties of ET-1. We therefore investigated the effects of intracoronary infusions of ET-1 and of the selective ETB receptor-selective agonist sarafotoxin 6c with increasing doses in anesthetized pigs. Myocardial effects were measured through analysis of the left ventricular pressure-volume relationship. ET-1 elicited increases in the myocardial contractile status (end-systolic elastance value of 0.94 ± 0.11 to 1.48 ± 0.23 and preload recruitable stroke work value of 68.7 ± 4.7 to 83.4 ± 7.2) that appear to be mediated through ETA receptors, whereas impairment in left ventricular isovolumic relaxation ({tau} = 41.5 ± 1.4 to 58.1 ± 5.0 and t1/2 = 23.0 ± 0.7 to 30.9 ± 2.6, where {tau} is the time constant for pressure decay and t1/2 is the half-time for pressure decay) was ETB receptor dependent. In addition, intravenous administration of ET-1 impaired ventricular relaxation but had no effect on contractility. Intracoronary sarafotoxin 6c administration caused impairments in left ventricular relaxation ({tau} from 43.3 ± 1.8 to 54.4 ± 3.4) as well as coronary vasoconstriction. In conclusion, ET-1 elicits positive inotropic and negative lusitropic myocardial effects in a pig model, possibly resulting from ETA and ETB receptor activation, respectively.

cardiac; inotropy; end-systolic elastance; diastolic; porcine; sarafotoxin

THE ENDOTHELINS ARE A FAMILY of 21 amino acid peptides with powerful vasoactive properties, which were first described in 1988 (48). Endothelin-1 (ET-1), which is probably the most important of the endothelins as far as effects in humans are concerned, is mainly produced by the vascular endothelium. This vasoconstrictive peptide acts on two groups of receptors: ETA and ETB receptors, located on vascular smooth muscle cells mediating contraction, and ETB receptors, located on the endothelium mediating vasodilation by release of nitric oxide and prostacyclin (1, 10, 31). In the heart, the predominant ET isopeptide is ET-1 (30), and both ETA and ETB receptor mRNA are found in atrial and ventricular myocardium, the conducting system, and endocardial cells as well as in coronary arteries (3, 26). The ET system and ET-1 binding properties on cardiomyocytes are largely similar in pigs and humans (25).

The ET system is involved in the cardiovascular response to several disease processes. Increased plasma levels of ET-1 have been noted in association with acute myocardial infarction, congestive heart failure, pulmonary hypertension, and septic shock (44). There are numerous reports regarding the cardiac effects of ET-1. The majority of studies done in larger animals or humans seems to indicate positive inotropic effects of ET-1 under nondisease conditions. Several studies have been performed in vitro in various species with conflicting results regarding myocardial effects (16, 21, 32, 34, 49). In these previous in vivo animal studies on cardiac effects of ET-1, the peptide has been administered intravenously. The potent vasoconstrictor properties of ET-1 may then have been confounding when myocardial effects have been assessed with load-dependent parameters.

The aim of the present study was to investigate the effects of cardiac ET receptor activation on left ventricular (LV) myocardial function. ET-1, which possesses a similar affinity for the ETA and ETB receptors, and sarafotoxin 6c (S6c), a selective ETB receptor agonist (46), were used for this purpose. These peptides were administered in low doses directly into the coronary circulation, and an intravenous dose was used as a reference. Furthermore, we assessed myocardial function through analysis of the LV pressure-volume relationship (LVPVR) to minimize loading confounders.


   MATERIALS AND METHODS
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 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
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The Research Ethical Committee at Umeå University approved the experimental protocol for this study, which was conducted in conformity with the European Convention for the protection of vertebrate animals used for experimentation and other scientific purposes (Council of Europe No. 123, Strasbourg 1985) and with the Guide for the Care and Use of Laboratory Animals (National Institutes of Health Publ. No. 85-23, Revised 1996).

Eleven female domestic land race pigs weighing between 33 and 44 kg were anesthetized after being fasted overnight with free access to water. After intramuscular injections of ketamine (10 mg/kg), azaperone (4 mg/kg), and atropine (50 µg/kg) were administered, anesthesia was induced with pentobarbital sodium (12 mg/kg iv) and maintained by a continuous infusion of pentobarbital sodium (5 mg·kg–1·h–1), midazolam (0.3 mg·kg–1·h–1), and fentanyl (20 µg·kg–1·h–1). Intravenous fluids were administered with the goal of maintaining normovolemia: Ringer acetate solution (25 ml/kg) during the first hour and thereafter (15 ml·kg–1·h–1) throughout the study period. After a tracheotomy was performed, the animals were mechanically ventilated (Servo 900B ventilator; Siemens Elema) to normoxia and normocapnea (Artema Medical, Stockholm, Sweden) with tidal volumes <10 ml/kg. Blood gas measurements were performed intermittently (ABL 5; Radiometer Copenhagen) to confirm capnography and pulse oximeter observations. Body temperature was measured and maintained between 38° and 39°C with the help of warmed intravenous fluids and a warming blanket.

All vascular catheters were placed through direct cutdowns onto the jugular or carotid vessels. A triple-lumen central venous catheter (Arrow International) and a thermistor-tipped pulmonary artery catheter (Optimetrix, Abbott) were placed as well as an arterial catheter with the tip in the descending aorta. A 7.5-Fr balloon occlusion catheter (Vascular Technologies, Solna, Sweden) was positioned in the inferior vena cava directly adjacent to the right atrium to provide a controlled transient restriction of venous return. Arterial, central venous, and pulmonary artery pressures were measured with the use of a fluid-filled catheter system and transducers (Gabarith PMSET; Becton Dickinson). A 7-Fr LV pigtail combination tip manometer and conductance catheter (CA-71083-PN; CD Leycom, Zoetermeer, Holland) was placed through an 8.5-Fr introducer in the carotid artery system into the LV with the use of fluoroscopic guidance. A dual thermistor-tipped coronary sinus catheter (Webster) was placed in the great cardiac vein (GCV). A guiding catheter (Guidant) was placed with the tip in the left main coronary artery for infusion of the drugs. The catheter position was checked and rechecked with the use of fluoroscopy and minimal amounts of intravascular radiographic contrast (Visipaque; Amersham, Solna, Sweden). An intravenous heparin infusion (1,000 IE/h) was started when the cardiac catheters were in place to minimize the risk of catheter-related thrombosis. At the conclusion of the experiment, the pigs were euthanized with an intravenous overdose combination of pentobarbital sodium bolus followed by a bolus of potassium.

Measurements and calculations. The conductance volumetry technique is well described elsewhere (37), and we have previously described this method in depth (7, 14). The LV volume was measured with a 12-electrode, dual-field conductance catheter with 8-mm spacing between electrodes and a signal conditioning amplifier (Leycom Sigma 5-DF; Cardiodynamics, Zoetermeer, Holland). The volume signal was calibrated with a stroke volume (SV) and flow reference ratio derived from thermodilution cardiac output (CO) measurements obtained with the use of the pulmonary artery catheter and a thermodilution computer (Wetenskappelijk Technische Institut, Rotterdam, Holland). Parallel conductance for the LV volume signal was measured with the hypertonic saline method (36). The LV pressure and conductance data were recorded with a sampling rate of 250 Hz with the use of a software package (PC Conduct, Cardiodynamics). All circulatory measurements were recorded and analyzed with the use of a digital signal acquisition and analysis software package (Acqknowledge; Biopac Systems, Santa Barbara, CA).

GCV flow (QGCV) was measured by thermodilution (4). Coronary O2 kinetics were calculated as follows: arterial O2 content = (arterial partial pressure O2 x 0.23) + hemoglobin concentration (1.39 x arterial O2 saturation); GCV O2 content = (GCV partial pressure O2 x 0.23) + hemoglobin concentration [1.39 x GCV O2 saturation (SGCVO2)]; LV O2 delivery (MDO2) = QGCV x arterial O2 content; LV myocardial O2 consumption (MO2) = (arterial O2 content – GCV O2 content) x QGCV; myocardial O2 extraction ratio = 100 x MO2/DO2. The unit for O2 content is milliliters per liter, and the unit for partial pressure is kilopascal.

The following general hemodynamic parameters for each point in the protocol were measured: heart rate (HR), mean arterial blood pressure (MAP), CO, SV, central venous pressure (CVP), mean pulmonary artery pressure (MPAP), LV end-systolic volume (LVEDV), LV end-diastolic pressure (LVEDP), LV maximal rate of change in pressure (dP/dtmax), and maximum negative rate of pressure change (dP/dtmin). End diastole was identified as the maximum LV volume before the isovolumic pressure increase, which was timed for the purpose of analysis of sequences with multiple heart cycles to 8–16 ms before the measured dP/dtmax or to 8–16 ms after the intracardiac ECG R wave. LV stroke work (SW) was measured from the integral of the pressure-volume area for each heart cycle. For each beat, the maximal instantaneous pressure-flow product during systole (Powermax) was calculated. The end-systolic points were initially estimated as maximal pressure-volume for each cycle, and these beats were used to establish an end-systolic PVR (ESPVR) for all beats with an x-intercept. A tangent to this x-intercept was then used to find a new end-systolic P-V point for all beats and a final ESPVR (18). End-systolic aortic elastance (Ea) was measured as end-systolic aortic pressure divided by SV. Ventricular-arterial coupling was calculated as end-systolic elastance (Ees) divided by Ea. Total potential energy [i.e., pressure-volume area (PVA)] was calculated for a single resting beat at the onset of a preload reduction sequence with the ESPVR and then (0.5)Pes(Ves – Vo), where Pes is LV end-systolic pressure, Ves is LV end-systolic volume, and Vo is the LV volume at the x-intercept for the ESPVR. SW was calculated for the same beat, and myocardial efficiency was expressed as SW/PVA, as well as single beat PVA/MO2 (38). For diastolic parameters, {tau} is the time constant for pressure decay during the isovolumic relaxation phase assuming a nonzero asymptote (8). Additionally, the half-time for pressure decay during isovolumic relaxation (t1/2) was measured (24). Also, for each measurement point in the protocol, a controlled preload alteration was performed during a brief period of apnea with transient inflation of the balloon-tipped catheter to occlude the inferior vena cava for a short period (6–8 s). A sequence of 6–12 contiguous heart cycles was later selected from this sequence for analysis on the basis of a progressive beat-to-beat reduction in the end-diastolic and end-systolic LV volumes. This sequence was analyzed for Ees (18) and preload recruitable SW (PRSW) (12). All myocardial function parameters were calculated with custom software.

Biochemical analyses. Plasma levels of ET-1-like immunoreactivity (ET-1 LI) were analyzed with radioimmunoassay as described by Hemsén (15). The cross-reactivity of the E1 antiserum used with other endothelins was 27% with ET-2, 8% with ET-3, and 0.03% with porcine Big ET-1. The cross-reactivity with S6c was 94%.

Experimental protocol. After completion of the preparation, a 45-min stabilization period was observed. After the baseline measurements were taken, an intracoronary infusion of ET-1 (Sigma) was started (n = 9 pigs). The dosage was increased at 30-min intervals (1, 2, 4, and 8 pmol·kg–1·min–1). All dosages were diluted to a volume of 50 ml with sodium chloride and infused into the left main coronary artery at a rate of 1.7 ml/min. Measurements were made after each dose during the last 10 min of the ongoing infusion. After a recovery period of 45 min, a 30-min intravenous infusion of ET-1 (10 pmol·kg–1·min–1) was followed with measurements made in the same fashion (n = 10 pigs). After another recovery period, an intracoronary infusion of S6c (Sigma) of 1 and 2 pmol·kg–1·min–1 took place in the same manner as described above (n = 10 pigs).

Statistical analysis. Data are presented as means ± SE. ANOVA was used to analyze changes over time from each control point to the last dose administered. For differences between doses compared with each control point, post hoc comparisons were made with the use of the Holm-Sidak method. The paired t-test was used for analysis of ET-1 given intravenously. Differences were considered significant at P < 0.05. A computer software program (SigmaStat 3.0; SPSS, Chicago, IL) was used for statistical calculations.


   RESULTS
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 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
LV contractile function. Intracoronary infusions of ET-1 evoked positive inotropic effects as demonstrated by increases in PRSW and Ees as well as dP/dtmax/EDV (Fig. 1 and Table 1). No changes in systolic function (Ees, PRSW, and dP/dtmax/EDV) were observed during intravenous ET-1, although a tendency toward a decrease in Powermax/EDV (P = 0.059) was noted (Table 2). S6c was associated with no change in Ees, a tendency toward a decrease in PRSW (P = 0.061), and decreases in Powermax/EDV as well as dP/dtmax/EDV during both doses (1 and 2 pmol·kg–1·min–1). Myocardial efficiency, expressed as SW/PVA, and MO2 both increased in response to intracoronary ET-1. PVA/MO2, the parameter for myocardial efficiency that considers oxygen consumption, did not change (tendency was toward a decrease; P = 0.056). Ventricular-arterial coupling (Ees/Ea) changed in the same direction. Myocardial efficiency (but not Ees/Ea) appeared to decrease a small amount during intravenous ET-1 (decrease in SW/PVA; no change in PVA/MO2). MO2 decreased during S6c infusion, although mechanical efficiency and Ees/Ea showed no consistent change.



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  		Fig. 1. Myocardial contractile function parameters: end-systolic elastance (Ees), preload recruitable stroke work (PRSW), maximal instantaneous pressure-flow product during systole/end-diastolic volume (Powermax/EDV), and left ventricular maximal rate of change in pressure (dP/dtmax)/EDV were studied after intracoronary endothelin-1 (ET-1; solid circles) infusion in nine pigs in increasing doses (1, 2, 4, and 8 pmol·kg–1·min–1). After recovery period, sarafotoxin 6c (S6c; open squares) was infused in 10 pigs in same manner with doses of 1 and 2 pmol·kg–1·min–1. Data are presented as means ± SE. Each dose was compared with its corresponding baseline value, and significant differences are displayed as follows: *P < 0.05; **P < 0.01; ***P < 0.001.

 

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  		Table 1. Descriptive circulatory parameters

 

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  		Table 2. Effects of intravenous infusion of ET-1

 
Diastole/isovolumic relaxation. Negative effects on isovolumic relaxation were observed with significant prolongations in {tau} and t1/2 at doses of 2, 4, and 8 pmol·kg–1·min–1 of ET-1 in the coronary circulation (Fig. 2). Both the doses of S6c as well as the systemic administration of ET-1 were associated with prolongations in {tau} and t1/2 (Table 2).



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  		Fig. 2. Isovolumic relaxation parameters: time constant for pressure decay ({tau}) and pressure half-time were studied after intracoronary ET-1 (solid circles) infusion in nine pigs in increasing doses (1, 2, 4, and 8 pmol·kg–1·min–1). After recovery period, S6c (open squares) was infused in 10 pigs in same manner with doses of 1 and 2 pmol·kg–1·min–1. Data are presented as means ± SE. Each dose was compared with its corresponding baseline value, and significant differences are displayed as follows: *P < 0.05; **P < 0.01; ***P < 0.001.

 
Descriptive circulatory parameters. Administration of ET-1 in the coronary circulation did not affect CO, HR, SV, or SW but caused an increase in CVP, MAP (4 and 8 pmol·kg–1·min–1), and MPAP (8 pmol·kg–1·min–1; Table 1). Increases in dP/dtmax were seen for 4 and 8 pmol·kg–1·min–1 of ET-1, whereas Powermax increased for 4 and 8 pmol·kg–1·min–1 of ET-1. With regard to diastolic effects, dP/dtmin was increased by 2, 4, and 8 pmol·kg–1·min–1 of ET-1. LVEDV was slightly increased at all doses, whereas LVEDP was unchanged.

Systemic administration of ET-1 caused decreases in CO, SV, and HR along with increases in MAP and CVP. MPAP and SW were not affected (Table 2). No effects were seen with regard to dP/dtmax or Powermax, whereas dP/dtmin decreased. An increase in LVEDP was also seen; however, LVEDV was unchanged.

Both doses of S6c in the coronary circulation were associated with decreases in CO, SV, and SW but had no effect on HR, MAP, MPAP, LVEDV, or LVEDP. CVP increased slightly by both 1 and 2 pmol·kg–1.·min–1, whereas dP/dtmax and Powermax were decreased and dP/dtmin was increased.

Coronary blood flow and oxygen utilization. QGCV was not affected during intracoronary ET-1 infusion (Table 1). However, MO2 increased with 2, 4, and 8 pmol·kg–1·min–1 of ET-1. There was no effect on QGCV by intravenous ET-1. The myocardial O2 extraction ratio increased in response to intravenous ET-1, although no statistical effects were seen regarding MDO2 or MO2. QGCV was decreased by S6c at both doses, with a more limited decrease by S6c in MO2 (2 pmol·kg–1·min–1).

Biochemical parameters. Increases in both arterial and GCV ET-1 LI plasma levels were seen in response to intracoronarily administered ET-1 at doses of 4 and 8 pmol·kg–1·min–1(Fig. 3). Intravenously administered ET-1 rendered equally high levels in arterial and GCV plasma. S6c caused increases in ET-1 LI plasma levels in the GCV; however, the cross-reactivity for S6c with ET-1 was 94%.



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  		Fig. 3. ET-1-like immunoreactivity (ET-1 LI) in arterial (solid circles) and great cardiac venous plasma (open squares) in nine pigs receiving ET-1 infusion of increasing doses (1, 2, 4, and 8 pmol·kg–1·min–1). After recovery period, ET-1 was administered intravenously to 10 pigs at 10 pmol·kg–1·min–1. After yet another recovery period, S6c was infused in 10 pigs in same manner with doses of 1 and 2 pmol·kg–1·min–1. C, control point. Data are presented as means ± SE. Each dose was compared with its corresponding baseline value, and significant differences for arterial ET-1 LI are displayed as follows: *P < 0.05; **P < 0.01; ***P < 0.001; significant differences for great cardiac vein ET-1-LI are displayed as follows: #P < 0.05; ###P < 0.001.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
The main effects seen in this study were enhanced myocardial contractile function by ET-1 and negative lusitropic effects by both ET-1 and S6c. The increases in myocardial contractility and measured ventricular performance with intracoronary ET-1 administration were accompanied by an increase in MO2. ET-1-related increases in the parameters of systolic function were derived from serial assessments of ventricular pressure-volume relations, allowing the detection of changes in myocardial contractile status independent of the prevailing loading conditions (17). The increases in Ees and PRSW induced by ET-1 were not seen when S6c was administered, suggesting that the enhanced contractile effects were related to ETA receptor activation.

It is currently believed that ETA receptor agonism subsequently results in the activation of protein kinase C that in turn increases the mobilization and reuptake of cytosolic Ca2+ and alters Ca2+ channel activity as well as enhances myofibrillar Ca2+ sensitivity via alkalization of the myocytes by Na+/H+ exchange (5, 47). In the present study, intracoronary ET-1 elicited positive effects on myocardial contractile status, seen as increases in Ees and PRSW. In healthy humans, ETA receptor agonism seems to provide a tonic positive contractile effect (23), and similar findings have been noted in an ex vivo model of perfused rat hearts where ET-1-induced positive LV contractile effects were abolished by an ETA receptor antagonist (40). In anesthetized pigs, ET-1 in combination with an ETB receptor antagonist caused similar positive inotropic effects as ET-1 infusion alone (9). The literature is, however, not uniform in this regard. Beyer et al. (6) used a selective ETB receptor agonist as well as ET-1 in combination with an ETA receptor antagonist in rats to demonstrate that ETB receptor activation was responsible for the myocardial contractile effects seen. The dosage used was, however, ~10 times higher than that in our study and was also administered intravenously, causing major vascular effects as well.

A rather recent study on an isolated rat heart model (40) demonstrated positive effects of ET-1 on myocardial efficiency with the use of PVA/MO2. We were unable to confirm these results with intracoronary ET-1 in the current study where the positive effects on contractility were accompanied by increased oxygen consumption. However, when expressing myocardial efficiency as SW/PVA and taking mechanical work into account, we see an increase in response to intracoronary ET-1.

In the current study, ETB receptor activation via intracoronary infusion of S6c did not cause significant changes in Ees or PRSW but decreased Powermax/EDV and dP/dtmax/EDV with unaltered MAP. This would suggest a mild negative effect on myocardial contractility related to ETB receptor activation. These findings are well in line with the effects seen in human LV myocytes (13). When administering S6c intravenously in anesthetized pigs, Cirino et al. (9) reported negative effects on myocardial contractile function (dP/dtmax and dP/dtmin); however, those findings were accompanied by a reduction in MAP of 60% (9).

S6c had profound negative lusitropic effects as shown by the changes in {tau} and t1/2 findings. These findings were accompanied by an attenuation of dP/dtmin. ET-1 intracoronary infusion caused an identical pattern in diastolic parameters, implying ETB receptor agonism as the mediator of the negative effect on LV isovolumic relaxation, as shown by Goldberg et al. (13) on human LV myocytes. In our study, S6c decreased QGCV and MO2 in connection with the negative diastolic effects, which for us awakened concern that severe coronary flow restriction could lead to an ischemic state with related myocardial dysfunction. The study design did not include methods to confirm or refute myocardial ischemia. However, ET-1 infusion did not affect QGCV and increased MO2 while causing the same diastolic effects as S6c, suggesting that mechanisms other than ischemia may be involved. Teerlink et al. (41) reported that intracoronary S6c had a transient vasodilatory effect in lower doses (up to 120 pmol) and a marked vasoconstricting effect in higher doses (up to 1,200 pmol) in open-chest dogs. These results agree with the findings where the lower dose of S6c (total of ~800 pmol) induced a >20% reduction in QGCV. This is likely explained by the activation of vascular smooth muscle ETB receptors (45).

Most in vivo studies on cardiac effects of ET-1 have used the intravenous route of administration. The vascular effects seen in response to systemic administration can affect the cardiac variables studied due to alterations in loading conditions. In the current study, the intravenous dose was used as a reference, where no effects were seen on the contractile function parameters (see Table 2), despite significant changes in MAP, CVP, and CO. This may suggest an increase in load and particularly afterload that could have elicited a baroreflex response, though no change in measured myocardial contractile status was noted. The differences in myocardial contractile effects for intravenous and intracoronary administration of ET-1 demonstrate the difficulty in assessing intrinsic myocardial function when using a highly potent vasoactive substance systemically. Moreover, the current study illustrates a clear advantage when using load-indexed measures of myocardial contractile status (Ees, PRSW, and Powermax/EDV) for interpreting direct myocardial effects in response to systemic administration.

Diastolic function parameters did not change during load alterations; both routes of administration produced similar results regarding {tau} and t1/2. QGCV was unchanged in response to intravenous ET-1. In a model with anesthetized pigs, Cirino et al. (9) infused 400 pmol/kg of ET-1 intravenously and noted transient decreases in MAP, dP/dtmax, and relaxation followed by increases in MAP, LVEDP, and dP/dtmax as well as a decrease in CO. Apart from the early transient effects, which we did not observe in our experiments, our observations agree with theirs, apart from dP/dtmax. They conclude after combining ET-1 with an ETB receptor antagonist that the positive inotropic effects were ETA receptor dependent. Our results, however, suggest that the major cardiac effects of intravenous ET-1 were mainly ETB receptor mediated. Furthermore, our findings are supported by a report from Kiely et al. (19), who, in a model of human volunteers, infused ET-1 intravenously at low doses and found an increase in LV isovolumic relaxation time or, in other words, negative lusitropy. They also reported negative effects on myocardial contractility of ET-1 in terms of reduced CO along with changes in electromechanical and Doppler acceleration indexes, which they admitted are highly loading condition dependent and were not taken into account. Those systolic function observations could be explained by changes in vascular tone and shifts in intravascular volumes, quite independent of myocardial contractile status. This, again, emphasizes the novelty of the results we have obtained in this context by using an invasive load-independent method of assessment of myocardial contractile status that is not readily available in healthy human volunteers. An alternative interpretation for the divergence of our systolic function results from those of Kiely et al. (19) is that pigs possibly respond differently to ET-1 than humans, though we know of no evidence to support this.

As expected, the intracoronary ET-1 infusion rendered a more pronounced increase in GCV plasma ET-1 LI than in arterial plasma. This difference was not noted with the intravenous infusion. An increase in ET-1 LI was also seen in response to S6c, a phenomenon explained by the high cross-reactivity of S6c to ET-1 (94%) in the radioimmunoassay used. The plasma levels noted in the GCV in the present study are high and by far exceed those observed in several other studies on failing hearts (4.7–15 pmol/l; Refs. 11 and 22). However, the relation between plasma levels and tissue concentrations or tissue activity of ET is complex. Several reports have described a preferential abluminal secretion of ET rather than intravasal by the endothelial cells (43). In a pathophysiological process where there is an increased local production of ET, the plasma levels constitute merely an indirect reflection of the local activity. This relation is confirmed by other investigators who assessed both plasma and tissue concentrations of ET (11). In fact, in a recent study on severely failing human hearts (33), cardiac tissue levels were approximately >500 pmol/kg. These reports are, however, limited to studies on endogenous ET. To our knowledge, no studies have been performed that look at the effects of exogenous ET administration on subsequent tissue concentrations. Therefore, it is difficult to anticipate the local ET receptor activity achieved in the myocardium in response to an infusion. Thus, although it could be argued that the concentrations achieved in the present study are pharmacological, their pathophysiological relevance may nonetheless be valid.

The data from the current study would suggest that ETA receptor agonism may be beneficial from a myocardial contractile function point of view and that ETB receptor antagonism may be useful for improving diastolic function. However, in pathophysiological states the situation seems to be far more complex. In induced congestive heart failure models, ET-1 seems to exert negative contractile effects (29, 42), hence the interest in using selective or nonselective ET receptor antagonists in clinical trials (35, 39). In healthy humans, ETA receptor agonism seems to provide enhanced myocardial contractile function, which does not occur in patients with dilated cardiomyopathy (23). Previous results from our own laboratory in which selective ETB receptor antagonism in septic pigs was used proved to be fatal, whereas dual ET receptor antagonism seems beneficial (20, 28). The mechanisms behind these apparent diverging results are not fully elucidated. Changes in receptor density as well as alterations in ETA-to-ETB receptor ratio may be involved (2). Furthermore, the cardiac unloading effects from vasodilation may result in overall beneficial hemodynamic responses, masking the potential negative inotropic effects seen in response to ET receptor antagonism in various conditions, such as sepsis (28).

Limitations.

This protocol was determined after pilot studies where the S6c-elicited effects on QGCV were evident. To avoid ischemic events potentially clouding the myocardial effects of ET-1, we decided not to perform the infusions in random order. Nonetheless, the recovery periods seem to have been adequate in the sense that plasma ET-1 LI concentrations returned to baseline levels before commencement of the postrecovery period infusion (Fig. 3). In addition, key cardiac parameters also returned to baseline values after each recovery period (Figs. 1 and 2).

The intracoronary infusions evoked minimal effects on systemic parameters; however, the doses chosen (based on the pilot study) rendered supranormal plasma concentrations of ET-1 LI in the GCV. However, ET-1 is normally secreted abluminally and acts from the interstitial side of the myocytes (43). Thus high doses may need to be administered to achieve relevant interstitial concentrations.

In conclusion, positive contractile effects of intracoronary ET-1 were observed through analysis of the LVPVR in this model, most probably mediated via ETA receptor activation. ET-1 also demonstrated negative lusitropic effects, as did S6c, suggesting an ETB-receptor-mediated negative diastolic function. These findings are strengthened by the use of this method of assessment of myocardial contractile function that is strongly resistant to changes in prevailing loading conditions, including ventricular loading changes brought about by vasoactive effects of ET-1. We conclude that ET-1 has acute positive inotropic effects in healthy in vivo myocardium. Further studies are warranted to understand the role of ET-1 in the regulation of myocardial function in pathophysiological states.


   GRANTS
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 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This study was supported by grants from the Swedish Heart Lung Foundation, the Swedish Research Council, and the Swedish Medical Society and by funds from the Karolinska Institute.


   FOOTNOTES
 

Address for reprint requests and other correspondence: D. Konrad, Dept. of Anaesthesiology and Intensive Care, Karolinska Hospital, SE17176 Stockholm, Sweden (david.konrad{at}kirurgi.ki.se)

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
 GRANTS
 REFERENCES
 

  1. Arai H, Hori S, Aramori I, Ohkubo H, and Nakanishi S. Cloning and expression of a cDNA encoding an endothelin receptor. Nature 348: 730–732, 1990.[CrossRef][Medline]
  2. Asano K, Bohlmeyer TJ, Westcott JY, Zisman L, Kinugawa K, Good M, Minobe WA, Roden R, Wolfel EE, Lindenfeld J, David Port J, Perryman MB, Clevel J, Lowes BD, and Bristow MR. Altered expression of endothelin receptors in failing human left ventricles. J Mol Cell Cardiol 34: 833–846, 2002.[CrossRef][Web of Science][Medline]
  3. Awane-Igata Y, Ikeda S, and Watanabe T. Inhibitory effects of TAK-044 on endothelin induced vasoconstriction in various canine arteries and porcine coronary arteries: a comparison with selective ETA and ETB receptor antagonists. Br J Pharmacol 120: 516–522, 1997.[CrossRef][Web of Science][Medline]
  4. Balfors E, Haggmark S, Ariola S Jr, Biber B, Ponten J, and Reiz S. In vitro analysis of thermal transport in coronary sinus thermodilution catheters. Clin Physiol 3: 469–476, 1983.[Web of Science][Medline]
  5. Baudet S, Weisser J, Janssen AP, Beulich K, Bieligk U, Pieske B, Noireaud J, Janssen PM, Hasenfuss G, and Prestle J. Increased basal contractility of cardiomyocytes overexpressing protein kinase C-{epsilon} and blunted positive inotropic response to endothelin-1. Cardiovasc Res 50: 486–494, 2001.[Abstract/Free Full Text]
  6. Beyer ME, Slesak G, Nerz S, Kazmaier S, and Hoffmeister HM. Effects of endothelin-1 and IRL 1620 on myocardial contractility and myocardial energy metabolism. J Cardiovasc Pharmacol 26, Suppl 3: S150–S152, 1995.
  7. Broome M, Haney M, Osterlund B, Haggmark S, Johansson G, and Biber B. The cardiac effects of intracoronary angiotensin II infusion. Anesth Analg 94: 787–793, 2002.[Abstract/Free Full Text]
  8. Brutsaert DL and Sys SU. Relaxation and diastole of the heart. Physiol Rev 69: 1228–1315, 1989.[Abstract/Free Full Text]
  9. Cirino M, Martin E, Yano M, and Rodger IW. Cardiovascular and renal actions of the endothelin(B) receptor in pigs. J Cardiovasc Pharmacol 29: 704–712, 1997.[CrossRef][Web of Science][Medline]
  10. de Nucci G, Thomas R, D’Orleans-Juste P, Antunes E, Walder C, Warner TD, and Vane JR. Pressor effects of circulating endothelin are limited by its removal in the pulmonary circulation and by the release of prostacyclin and endothelium-derived relaxing factor. Proc Natl Acad Sci USA 85: 9797–9800, 1988.[Abstract/Free Full Text]
  11. Ergul A, Walker CA, Goldberg A, Baicu SC, Hendrick JW, King MK, and Spinale FG. ET-1 in the myocardial interstitium: relation to myocyte ECE activity and expression. Am J Physiol Heart Circ Physiol 278: H2050–H2056, 2000.[Abstract/Free Full Text]
  12. Glower DD, Spratt JA, Snow ND, Kabas JS, Davis JW, Olsen CO, Tyson GS, Sabiston DC Jr, and Rankin JS. Linearity of the Frank-Starling relationship in the intact heart: the concept of preload recruitable stroke work. Circulation 71: 994–1009, 1985.[Abstract/Free Full Text]
  13. Goldberg AT, Bond BR, Mukherjee R, New RB, Zellner JL, Crawford FA Jr, and Spinale FG. Endothelin receptor pathway in human left ventricular myocytes: relation to contractility. Ann Thorac Surg 69: 711–716, 2000.[Abstract/Free Full Text]
  14. Haney MF, Johansson G, Haggmark S, and Biber B. Method of preload reduction during LVPVR analysis of systolic function: airway pressure elevation and vena cava occlusion. Anesthesiology 97: 436–446, 2002.[CrossRef][Web of Science][Medline]
  15. Hemsén A. Biochemical and functional characterization of endothelin peptides with special reference to vascular effects. Acta Physiol Scand Suppl 602: 1–61, 1991.[Medline]
  16. Ishikawa T, Li LM, Shinmi O, Kimura S, Yanagisawa M, Goto K, and Masaki T. Characteristics of binding of endothelin-1 and endothelin-3 to rat hearts. Developmental changes in mechanical responses and receptor subtypes. Circ Res 69: 918–926, 1991.[Abstract/Free Full Text]
  17. Kass DA and Maughan WL. From "Emax" to pressure-volume relations: a broader view. Circulation 77: 1203–1212, 1988.[Free Full Text]
  18. Kass DA, Maughan WL, Guo ZM, Kono A, Sunagawa K, and Sagawa K. Comparative influence of load versus inotropic states on indexes of ventricular contractility: experimental and theoretical analysis based on pressure-volume relationships. Circulation 76: 1422–1436, 1987.[Abstract/Free Full Text]
  19. Kiely DG, Cargill RI, Struthers AD, and Lipworth BJ. Cardiopulmonary effects of endothelin-1 in man. Cardiovasc Res 33: 378–386, 1997.[Abstract/Free Full Text]
  20. Konrad D, Oldner A, Rossi P, Wanecek M, Rudehill A, and Weitzberg E. Differentiated and dose-related cardiovascular effects of a dual endothelin receptor antagonist in endotoxin shock. Crit Care Med 32: 1192–1199, 2004.[CrossRef][Web of Science][Medline]
  21. Kramer 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]
  22. Lerman A, Kubo SH, Tschumperlin LK, and Burnett JC Jr. Plasma endothelin concentrations in humans with end-stage heart failure and after heart transplantation. J Am Coll Cardiol 20: 849–853, 1992.[Abstract]
  23. MacCarthy PA, Grocott-Mason R, Prendergast BD, and Shah AM. Contrasting inotropic effects of endogenous endothelin in the normal and failing human heart: studies with an intracoronary ETA receptor antagonist. Circulation 101: 142–147, 2000.[Abstract/Free Full Text]
  24. Mirsky I. Assessment of diastolic function: suggested methods and future considerations. Circulation 69: 836–841, 1984.[Free Full Text]
  25. Modesti PA, Vanni S, Paniccia R, Perna A, Maccherini M, Lisi G, Sani G, and Neri Serneri G. Endothelin receptors in adult human and swine isolated ventricular cardiomyocytes. Biochem Pharmacol 58: 369–374, 1999.[CrossRef][Web of Science][Medline]
  26. 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]
  27. Nakayama M, Chen CH, Nevo E, Fetics B, Wong E, and Kass DA. Optimal preload adjustment of maximal ventricular power index varies with cardiac chamber size. Am Heart J 136: 281–288, 1998.[CrossRef][Web of Science][Medline]
  28. Oldner A, Wanecek M, Weitzberg E, Sundin P, Sollevi A, Rubio C, Hellstrom PM, Alving K, and Rudehill A. Differentiated effects on splanchnic homeostasis by selective and non-selective endothelin receptor antagonism in porcine endotoxaemia. Br J Pharmacol 127: 1793–1804, 1999.[CrossRef][Web of Science][Medline]
  29. Pearl JM, Nelson DP, Wagner CJ, Lombardi JP, and Duffy JY. Endothelin receptor blockade reduces ventricular dysfunction and injury after reoxygenation. Ann Thorac Surg 72: 565–570, 2001.[Abstract/Free Full Text]
  30. Plumpton C, Ferro CJ, Haynes WG, Webb DJ, and Davenport AP. The increase in human plasma immunoreactive endothelin but not big endothelin-1 or its C-terminal fragment induced by systemic administration of the endothelin antagonist TAK-044. Br J Pharmacol 119: 311–314, 1996.[Web of Science][Medline]
  31. Pollock DM and Opgenorth TJ. Evidence for endothelin-induced renal vasoconstriction independent of ETA receptor activation. Am J Physiol Regul Integr Comp Physiol 264: R222–R226, 1993.[Abstract/Free Full Text]
  32. Qi XL, Sia YT, Stewart DJ, Wei G, Nguyen QT, Cernacek P, Picard P, Sirois M, and Rouleau JL. Myocardial contractile responsiveness to endothelin-1 in the postinfarction rat model of heart failure: effects of chronic quinapril. J Mol Cell Cardiol 33: 2023–2035, 2001.[CrossRef][Web of Science][Medline]
  33. Ry SD, Andreassi MG, Clerico A, Biagini A, and Giannessi D. Endothelin-1, endothelin-1 receptors and cardiac natriuretic peptides in failing human heart. Life Sci 68: 2715–2730, 2001.[CrossRef][Web of Science][Medline]
  34. Sakurai K, Norota I, Tanaka H, Kubota I, Tomoike H, and Endo M. Negative inotropic effects of angiotensin II, endothelin-1 and phenylephrine in indo-1 loaded adult mouse ventricular myocytes. Life Sci 70: 1173–1184, 2002.[CrossRef][Web of Science][Medline]
  35. Spieker LE, Mitrovic V, Noll G, Pacher R, Schulze MR, Muntwyler J, Schalcher C, Kiowski W, and Luscher TF, and ET 003 Investigators. Acute hemodynamic and neurohumoral effects of selective ETA receptor blockade in patients with congestive heart failure. J Am Coll Cardiol 35: 1745–1752, 2000.[Abstract/Free Full Text]
  36. Steendijk P, Staal E, Jukema JW, and Baan J. Hypertonic saline method accurately determines parallel conductance for dual-field conductance catheter. Am J Physiol Heart Circ Physiol 281: H755–H763, 2001.[Abstract/Free Full Text]
  37. Steendijk P, Van der Velde ET, and Baan J. Left ventricular stroke volume by single and dual excitation of conductance catheter in dogs. Am J Physiol Heart Circ Physiol 264: H2198–H2207, 1993.[Abstract/Free Full Text]
  38. Suga H. Ventricular energetics. Physiol Rev 70: 247–277, 1990.[Free Full Text]
  39. Sutsch G, Kiowski W, Yan XW, Hunziker P, Christen S, Strobel W, Kim JH, Rickenbacher P, and Bertel O. Short-term oral endothelin-receptor antagonist therapy in conventionally treated patients with symptomatic severe chronic heart failure. Circulation 98: 2262–2268, 1998.[Abstract/Free Full Text]
  40. Takeuchi Y, Kihara Y, Inagaki K, Yoneda T, and Sasayama S. Endothelin-1 has a unique oxygen-saving effect by increasing contractile efficiency in the isolated rat heart. Circulation 103: 1557–1563, 2001.[Abstract/Free Full Text]
  41. Teerlink JR, Breu V, Sprecher U, Clozel M, and Clozel JP. Potent vasoconstriction mediated by endothelin ETB receptors in canine coronary arteries. Circ Res 74: 105–114, 1994.[Abstract/Free Full Text]
  42. Thomas PB, Liu EC, Webb ML, Mukherjee R, Hebbar L, and Spinale FG. Exogenous effects and endogenous production of endothelin in cardiac myocytes: potential significance in heart failure. Am J Physiol Heart Circ Physiol 271: H2629–H2637, 1996.[Abstract/Free Full Text]
  43. Wagner OF, Christ G, Wojta J, Vierhapper H, Parzer S, Nowotny PJ, Schneider B, Waldhausl W, and Binder BR. Polar secretion of endothelin-1 by cultured endothelial cells. J Biol Chem 267: 16066–16068, 1992.[Abstract/Free Full Text]
  44. Wanecek M, Weitzberg E, Rudehill A, and Oldner A. The endothelin system in septic and endotoxin shock. Eur J Pharmacol 407: 1–15, 2000.[CrossRef][Web of Science][Medline]
  45. Warner TD, Allcock GH, Corder R, and Vane JR. Use of the endothelin antagonists BQ-123 and PD 142893 to reveal three endothelin receptors mediating smooth muscle contraction and the release of EDRF. Br J Pharmacol 110: 777–782, 1993.[Web of Science][Medline]
  46. Williams DL Jr, Jones KL, Pettibone DJ, Lis EV, and Clineschmidt BV. Sarafotoxin S6c: an agonist which distinguishes between endothelin receptor subtypes. Biochem Biophys Res Commun 175: 556–561, 1991.[CrossRef][Web of Science][Medline]
  47. Woo SH and Lee CO. Effects of endothelin-1 on Ca2+ signaling in guinea-pig ventricular myocytes: role of protein kinase C. J Mol Cell Cardiol 31: 631–643, 1999.[CrossRef][Web of Science][Medline]
  48. Yanagisawa M, Inoue A, Ishikawa T, Kasuya Y, Kimura S, Kumagaye S, Nakajima K, Watanabe TX, Sakakibara S, Goto K, and Masaki M. Primary structure, synthesis, and biological activity of rat endothelin, an endothelium-derived vasoconstrictor peptide. Proc Natl Acad Sci USA 85: 6964–6967, 1988.[Abstract/Free Full Text]
  49. Yang HT, Sakurai K, Sugawara H, Watanabe T, Norota I, and Endoh M. Role of Na+/Ca2+ exchange in endothelin-1-induced increases in Ca2+ transient and contractility in rabbit ventricular myocytes: pharmacological analysis with KB-R7943. Br J Pharmacol 126: 1785–1795, 1999.[CrossRef][Web of Science][Medline]



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D. Konrad, M. Haney, G. Johansson, M. Wanecek, E. Weitzberg, and A. Oldner
Cardiac effects of endothelin receptor antagonism in endotoxemic pigs
Am J Physiol Heart Circ Physiol, August 1, 2007; 293(2): H988 - H996.
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