AJP - Heart Calcium Transients and Cell-Sarcomere
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Heart Circ Physiol 287: H1476-H1483, 2004. First published June 17, 2004; doi:10.1152/ajpheart.00297.2004
0363-6135/04 $5.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
287/4/H1476    most recent
00297.2004v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Okajima, M.
Right arrow Articles by Lavallée, M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Okajima, M.
Right arrow Articles by Lavallée, M.

Pathophysiological plasma ET-1 levels antagonize {beta}-adrenergic dilation of coronary resistance vessels in conscious dogs

Masaki Okajima,1 Robert Parent,1 Eric Thorin,1,3 and Michel Lavallée1,2

1Institut de Cardiologie de Montréal and Departments of 2Physiology and 3Surgery, Faculty of Medicine, Université de Montréal, Montreal, Quebec, Canada H1T 1C8

Submitted 1 April 2004 ; accepted in final form 10 June 2004


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
On the basis of in vitro experiments showing that endothelin (ET)-1 interferes with smooth muscle ATP-sensitive K+ (KATP) channel opening, which is pivotal in {beta}-adrenergic coronary dilation, we hypothesized that pathophysiological plasma ET-1 levels impair {beta}-adrenergic dilation of resistance coronary vessels. In conscious instrumented dogs, graded intravenous doses of dobutamine caused the expected inotropic responses. As myocardial O2 consumption (MO2) increased, the disproportionate rise in coronary sinus (CS) PO2 indicates that increases in coronary blood flow (CBF) exceeded metabolic requirements, consistent with {beta}-adrenergic dilation. ET-1 intravenous infusions, to reach pathophysiological plasma levels, reduced slopes of the PO2-MO2 and CBF-MO2 relations. In contrast, the first derivative of left ventricular pressure over time responses to dobutamine were not impaired during ET-1 delivery. Clazosentan, an ETA receptor blocker, prevented reduction of the slope of PO2-MO2 and CBF-MO2 relations. After ganglionic blockade to exclude reflex influences, ET-1 still reduced slopes of PO2-MO2 and CBF-MO2 relations. To assess effects of ET-1 on endothelium-dependent and -independent coronary vascular responses, intracoronary ACh and nitroglycerin were given to directly target coronary vessels. CBF responses to ACh and nitroglycerin were maintained during ET-1 delivery. In contrast, responses to intracoronary KATP channel-dependent dilators adenosine and lemakalim were impaired by ET-1. In conclusion, pathophysiological levels of ET-1 impaired {beta}-adrenergic dilation of resistance coronary vessels through an ETA receptor-dependent process. In contrast, left ventricular inotropic responses to dobutamine were not impaired during ET-1 delivery. Our data suggest that ET-1 may interfere with smooth muscle KATP channels to impair {beta}-adrenergic coronary dilation.

endothelin-1; coronary blood flow; dobutamine; ATP-dependent potassium channels; myocardial oxygen consumption

PLASMA ENDOTHELIN (ET)-1 levels are elevated in human heart failure (1, 6, 13, 20, 24) and pulmonary hypertension (33). The pulmonary circulation acts as the primary source of circulating ET-1 (5, 24). Even if local ET-1 activity is increased in failing hearts (2), circulating ET-1 is still being extracted by the heart, which acts as a consumer, rather than a producer, of circulating ET-1 (5, 24). In humans, increases in circulating ET-1 levels within the pathophysiological range led to decreases in coronary sinus (CS) blood flow and venous blood O2 saturation, consistent with coronary constriction (19). In normal conscious pigs (14, 15) and dogs (26), blockade of ET-1 receptors led to increases in coronary venous blood O2 saturation. Thus ET-1 activity may reach the threshold for altering myocardial O2 supply-demand balance in normal and pathophysiological states.

In the setting of heart failure, the neurohormonal response involves concomitant increases in {beta}-adrenergic receptor activation and circulating ET-1 levels. The fact that, in vitro, ET-1 inhibits isoproterenol-stimulated cAMP accumulation in cardiomyocytes (10, 30) and pericardial smooth muscle cells (34) raises the possibility of a cross talk between {beta}-adrenergic and ET-1 receptors, ETA receptors in particular. In support of that possibility, ET-1 has been shown in isolated vessels to blunt the opening of ATP-sensitive K+ (KATP) channels (18), which is pivotal in {beta}-adrenergic dilation of resistance coronary vessels (16). Given that {beta}-adrenergic receptor activation acts as a feedforward mechanism to cause coronary dilation in the face of heightened sympathetic activity (7), a blunted {beta}-adrenergic coronary dilation caused by ET-1 would be expected to unfavorably alter the match between myocardial O2 supply and demand.


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Instrumentation. After general anesthesia with pentobarbital sodium (30 mg/kg iv) and under sterile conditions, 19 mongrel dogs (30 ± 2 kg) underwent a left thoracotomy at the fifth intercostal space under artificial ventilation. The pericardium was widely incised parallel to the phrenic nerve. A Tygon (Norton Plastics and Synthetic Division) catheter was implanted in the thoracic aorta to measure arterial pressure via an external transducer (model 800, Bentley Trantec). Mean arterial pressure (MAP) was obtained with an active filter with a time constant of 2 s. Through an apical stab wound, a solid-state pressure transducer (model P6.5, Konigsberg Instruments) was inserted in the left ventricular (LV) cavity to record LV pressure (LVP) and its first derivative over time (LV dP/dt). A catheter was also implanted in the LV to cross calibrate the miniature pressure gauge and to eliminate any drift of the instrument through repeated calibrations. Additional catheters were implanted in the right atrium (RA) and in the proximal pulmonary artery (PA). A cardiotachometer (model 9857, Sensor Medics) triggered by LVP was used to monitor heart rate (HR). An ultrasonic Doppler blood flow transducer was placed around the circumflex coronary artery, 1–2 cm from the bifurcation of the left main coronary artery. Coronary blood flow (CBF) was monitored using a 10-MHz pulsed Doppler flowmeter. Mean CBF was obtained with an active filter with a time constant of 2 s. A Silastic (Dow Corning) catheter was implanted in the CS. The tip of the catheter was ≥1 cm from the CS ostium. The position of the CS catheter was confirmed at necropsy. The pericardium was loosely closed, the chest was closed in layers, and the catheters and wires were exteriorized on the back of the animals. Analgesia was provided postoperatively with buprenorphine (0.3 mg im; Reckitt and Colman Pharmaceuticals). Prophylactic procaine penicillin G (300,000 units im) and benzathine penicillin G (300,000 units im) were administered for 10 days after the surgery.

Hemodynamic variables were recorded on a VHS tape via a PCM recording adaptor (model 4000A, Vetter) and monitored on a direct ink-writing strip chart recorder (model 2800s, Gould).

Protocols. Experiments were initiated 2–4 wk after surgery in conscious healthy dogs lying on a table of a dimly illuminated laboratory. While the dogs were resting quietly, hemodynamic variables were continuously monitored until a stable baseline was reached. At that time, blood samples (1 ml) were simultaneously withdrawn in lightly heparinized syringes from the aortic and CS catheters to measure hemoglobin (Hb) concentration, PO2, and Hb O2 saturation. An additional arterial blood sample (3 ml) was transferred to chilled tubes containing EDTA and placed on ice for later ET-1 determinations. These samples were centrifuged at 3,000 rpm and 3°C, and the plasma was collected and stored at –70°C until the day of the assay. ET-1 was measured with a sensitive and specific ELISA (Biomedica). Hb concentration, Hb O2 saturation, and PO2 were measured immediately after blood collection. A CO-oximeter (model OSM-2, Radiometer) was used to measure Hb concentration and Hb O2 saturation. PO2 was measured on a Stat Profile pHOx analyzer (Nova Biomedical).

Dobutamine hydrochloride (Sabex), a {beta}-adrenergic agonist, was administered through the PA catheter at 2.5, 5.0, and 7.5 µg·kg–1·min–1 until a steady state was reached (4–6 min); CS and aortic blood samples were then collected for blood gas analysis. The same protocol was repeated during ET-1 (2.5 ng·kg–1·min–1; American Peptide) delivery (n = 7) through the RA catheter. In all experiments, ET-1 was delivered for 30 min before the beginning of dobutamine infusions and maintained thereafter. Arterial blood samples for ET-1 measurements were obtained 30 min after the beginning of ET-1 delivery and at the completion of dobutamine infusions. This ensured that steady-state plasma ET-1 levels were reached during exogenous ET-1 delivery. On a separate day, dobutamine infusions were made 30 min after the beginning of a continuous RA infusion of ET-1 (4.0 ng·kg–1·min–1, n = 8). In additional experiments (n = 8), dobutamine was infused through the PA during delivery of ET-1 (4.0 ng·kg–1·min–1) through the RA after administration of clazosentan (Actelion), an ETA receptor blocker (21). Clazosentan was delivered through a peripheral vein as a priming dose of 50.0 µg·kg–1·min–1 for 10 min followed by 5.0 µg·kg–1·min–1 for the duration of the experiments. In additional experiments (n = 7), dobutamine was administered before and 30 min after the beginning of a continuous clazosentan infusion.

In additional experiments (n = 6), dobutamine was administered before and 30 min after the beginning of a continuous RA infusion of ET-1 (4.0 ng·kg–1·min–1) after ganglionic blockade with RA infusions of hexamethonium bromide (35.0 mg/kg; Sigma) and methyl atropine (0.1 mg/kg; Sigma). In additional dogs (n = 6) instrumented as described above (without the CS catheter), a Silastic catheter was implanted in the lumen of the proximal circumflex coronary artery, upstream from the Doppler flow probe. The portion of the catheter within the coronary vessel had an external diameter of 0.6 mm. Intracoronary boluses of acetylcholine chloride (ACh, 1.0 and 3.0 ng/kg; Sigma) and nitroglycerin (NTG, 100.0 ng/kg; Parke-Davis) were administered before and 30 min after the beginning of a continuous RA infusion of ET-1 (4.0 ng·kg–1·min–1). In five of these dogs, intracoronary infusions of adenosine (250, 500, and 750 ng·kg–1·min–1 for 4–6 min; Sigma) were made before and 30 min after the beginning of a continuous RA infusion of ET-1 (4.0 ng·kg–1·min–1). In five additional dogs with intracoronary catheters, lemakalim (SmithKline Beecham Pharma), a KATP channel opener, was delivered as intracoronary boluses (50, 75, and 100 ng/kg) before and 30 min after the beginning of a continuous RA infusion of ET-1 (4.0 ng·kg–1·min–1).

Data analysis. Values are means ± SE. Myocardial O2 consumption (MO2) is the difference between aorta and CS O2 content times CBF (in ml·min–1·g tissue–1). Coronary vascular resistance (CVR) is the ratio of MAP to CBF. A one-way analysis of variance for repeated measurements was used to compare variables with baseline. A two-way analysis of variance was used for simultaneous overall comparisons of dobutamine, ACh, adenosine, or lemakalim responses before and after treatment. Post hoc comparisons were made with the Newman-Keuls test to isolate specific contrasts. Slopes of relations between MO2 and CS PO2 or CBF were established for each animal and compared with an analysis of variance or a paired t-test. Paired t-tests were used when NTG-induced CBF responses before and after ET-1 were compared. Statistical significance was reached when P < 0.05 in all cases. All experimental procedures were performed in accordance with institutional guidelines.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Dobutamine with or without ET-1 delivery. Under control conditions, dobutamine increased LVP, LV dP/dt, MAP, and HR (Tables 1 and 2). As a consequence of changes in the determinants of cardiac metabolic demand, cardiac MO2 and CBF increased. The rise in CS PO2 concomitant with the increase in MO2 indicates that CBF was in excess of cardiac metabolic requirements during dobutamine delivery. Therefore, dobutamine had significant dilator effects in addition to its metabolic activity. The hemodynamic effects of dobutamine and the slope of the relations between CS PO2 or CBF and MO2 did not significantly differ before the various interventions, i.e., before ET-1 (2.5 and 4.0 ng·kg–1·min–1), clazosentan, or ET-1 + clazosentan.


View this table:
[in this window]
[in a new window]
  		Table 1. Effects of ET-1 on hemodynamic responses to graded doses of dobutamine

 

View this table:
[in this window]
[in a new window]
  		Table 2. Effects of ET-1 on hemodynamic responses to graded doses of dobutamine before and after clazosentan

 
Table 1 reports the hemodynamic effects of graded doses of dobutamine before and during ET-1 (2.5 ng·kg–1·min–1). ET-1 increased baseline MAP and CVR and decreased LV dP/dt and HR. Except for increases in CS PO2 caused by dobutamine that were smaller during ET-1 (2.5 ng·kg–1·min–1) than before ET-1, other hemodynamic responses did not differ before and during ET-1. The slopes of the relations between CS PO2 or CBF and MO2 were reduced during dobutamine + ET-1; i.e., for any given increase in MO2 caused by dobutamine, PO2 and CBF increased less during ET-1 than before ET-1 (Fig. 1). Thus ET-1 impaired coronary dilator effects of dobutamine.



View larger version (16K):
[in this window]
[in a new window]
  		Fig. 1. Coronary sinus (CS) PO2-myocardial O2 consumption (MO2; A) and coronary blood flow (CBF)-MO2 (B) relations during graded doses of dobutamine before and during endothelin (ET)-1 (2.5 ng·kg–1·min–1 iv) delivery. Statistical differences between slopes are reported. ET-1 reduced slopes of the relations.

 
Table 2 reports the hemodynamic effects of graded doses of dobutamine before and during ET-1 (4.0 ng·kg–1·min–1). ET-1 increased LVP, MAP, and CVR and decreased HR. Dobutamine-induced LV dP/dt responses were increased during ET-1 (4.0 ng·kg–1·min–1), whereas CS PO2 responses were decreased. The slopes of the relations between CS PO2 or CBF and MO2 were reduced during dobutamine + ET-1 (Fig. 2). Baseline arterial plasma ET-1 levels averaged 0.5 ± 0.1 fmol/ml. ET-1 delivery (2.5 and 4.0 ng·kg–1·min–1) increased (P < 0.01) plasma levels to 3.4 ± 0.5 (n = 7) and 7.2 ± 1.1 (n = 8) fmol/ml, respectively, after 30 min. A steady-state plasma ET-1 level was maintained thereafter (Fig. 3). Data for ET-1 (4.0 ng·kg–1·min–1) at the completion of the experiments were available in six dogs.



View larger version (17K):
[in this window]
[in a new window]
  		Fig. 2. CS PO2-MO2 (A) and CBF-MO2 (B) relations during graded doses of dobutamine before and during ET-1 (4.0 ng·kg–1·min–1 iv) delivery with or without ETA receptor blockade (clazosentan). Statistically different from control: *P < 0.05; {dagger}P < 0.01. ET-1 reduced slopes of the relations; ETA receptor blockade prevented ET-1-induced reduction of slopes.

 


View larger version (14K):
[in this window]
[in a new window]
  		Fig. 3. Arterial plasma ET-1 levels before ET-1 delivery (baseline), after 30 min of ET-1 delivery (2.5 and 4.0 ng·kg–1·min–1 iv), and at completion of experiments (end). Data are reported in 7 dogs for low dose of ET-1 and in 6 dogs for high dose of ET-1. *P < 0.01 vs. baseline. ET-1 plasma levels at 30 min and at end did not significantly differ.

 
Dobutamine + ET-1 delivery with or without blockade of ETA receptors. Clazosentan + ET-1 resulted in lower baseline LVP and MAP and higher HR than ET-1 alone. LV dP/dt responses to dobutamine were reduced and CS PO2 responses were increased during ET-1 (4.0 ng·kg–1·min–1) + clazosentan compared with ET-1 alone. Other hemodynamic responses to dobutamine did not differ from those observed with ET-1 alone (Table 2). The slopes of the relations between CS PO2 or CBF and MO2 during dobutamine after ET-1 + clazosentan did not significantly differ from those after dobutamine alone (Fig. 2).

Blockade of ETA receptors alone. The slopes of the relations between CS PO2 or CBF and MO2 during dobutamine delivery did not statistically differ before and after clazosentan. Clazosentan increased (P < 0.01) plasma ET-1 levels from 0.6 ± 0.1 to 1.8 ± 0.2 fmol/ml.

Ganglionic blockade + dobutamine with or without ET-1. After ganglionic blockade, dobutamine caused greater (P < 0.05) dose-dependent increases in MO2 with ET-1 (4.0 ng·kg–1·min–1) than without ET-1. The slopes of the relations between CS PO2 or CBF and MO2 during dobutamine were reduced (P < 0.05) after ET-1, consistent with impaired dilator effects (Fig. 4). ET-1 did not significantly alter baseline LV dP/dt (from 2,501 ± 135 to 2,308 ± 49 mmHg/s). Before ET-1, dobutamine-induced LV dP/dt increases averaged 1,261 ± 170, 2,566 ± 314, and 3,653 ± 365 mmHg/s at 2.5, 5.0, and 7.5 µg·kg–1·min–1, respectively. During ET-1, LV dP/dt responses to 2.5, 5.0, and 7.5 µg·kg–1·min–1 dobutamine averaged 1,419 ± 180, 3,097 ± 355, and 4,453 ± 395 mmHg/s, respectively, with greater (P < 0.01) responses than before ET-1 for the two higher doses of dobutamine.



View larger version (18K):
[in this window]
[in a new window]
  		Fig. 4. CS PO2-MO2 (A) and CBF-MO2 (B) relations during graded doses of dobutamine before and during ET-1 (4.0 ng·kg–1·min–1 iv) delivery after ganglionic blockade. Statistical differences between slopes are reported. ET-1 reduced slopes of relations.

 
Nitric oxide-dependent responses with and without ET-1. Endothelium-dependent and -independent responses to intracoronary boluses of ACh and NTG, respectively, were compared before and during ET-1 (4.0 ng·kg–1·min–1) in six dogs. Baseline CBF was not significantly altered by ET-1. ET-1 did not interfere with peak, volume, or duration of CBF responses triggered by intracoronary ACh and NTG (Fig. 5). ACh and NTG had no other hemodynamic effects.



View larger version (15K):
[in this window]
[in a new window]
  		Fig. 5. A: CBF before (baseline) and at peak effects of intracoronary boluses of acetylcholine (ACh) and nitroglycerin (NTG) before and during ET-1 (4.0 ng·kg–1·min–1 iv). B and C: volume (area under CBF responses) and duration (time from rise to return to baseline CBF) of CBF responses. ET-1 did not significantly alter baseline CBF; ACh and NTG responses did not statistically differ before and after ET-1. *P < 0.01 vs. baseline.

 
Adenosine with or without ET-1. Intracoronary adenosine was delivered before and during ET-1 (4.0 ng·kg–1·min–1) in five dogs. The effects of adenosine were limited to changes in CBF. Baseline CBF was not significantly altered by ET-1. Adenosine-induced increases in CBF were substantially reduced by ET-1 (Fig. 6).



View larger version (14K):
[in this window]
[in a new window]
  		Fig. 6. Baseline and steady-state CBF achieved during intracoronary (ic) adenosine infusions before and during ET-1 (4.0 ng·kg–1·min–1 iv) delivery. ET-1 caused a substantial reduction of CBF responses to adenosine but failed to significantly alter baseline CBF. *P < 0.05; {dagger}P < 0.01 vs. baseline.

 
Lemakalim with or without ET-1. Intracoronary boluses of lemakalim were delivered before and during ET-1 (4.0 ng·kg–1·min–1) in five additional dogs. The effects of lemakalim were limited to changes in CBF. Baseline CBF was not significantly altered by ET-1. ET-1 reduced peak, volume, and duration of CBF responses triggered by intracoronary lemakalim (Fig. 7).



View larger version (17K):
[in this window]
[in a new window]
  		Fig. 7. A: CBF before (baseline) and at peak effects of intracoronary boluses of lemakalim before and during ET-1 (4.0 ng·kg–1·min–1 iv) delivery. B and C: volume (area under CBF responses) and duration (time from rise to return to baseline CBF) of CBF responses. ET-1 did not significantly alter baseline CBF; lemakalim-induced CBF responses were reduced by ET-1. *P < 0.01 vs. baseline. {dagger}P < 0.05; {ddagger}P < 0.01 vs. control.

 

   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
The main finding of the present study is that plasma ET-1 within the pathophysiological range impairs {beta}-adrenergic dilation of resistance coronary vessels caused by dobutamine in conscious dogs. In contrast, ET-1 failed to impair dobutamine-induced LV positive inotropic responses. Blockade of ETA receptors prevented the inhibitory action of ET-1 on {beta}-adrenergic coronary dilation. Our data after ganglionic blockade indicate that reflex mechanisms were not involved in the cross talk between ET-1 and {beta}-adrenergic receptors. The lack of inhibitory effects of ET-1 on ACh- and NTG-induced dilation of resistance coronary vessels excludes nitric oxide (NO) as a key intermediate in the {beta}-adrenergic receptor-ET-1 interaction. Our data showing that ET-1 also antagonized responses to the KATP channel-dependent dilators adenosine and lemakalim are consistent with the involvement of these channels in the ET-1-{beta}-adrenergic receptor cross talk in the coronary microcirculation.

In the present study, our selection of doses of ET-1 for systemic delivery was guided by earlier studies showing that ET-1 at 2.5 ng·kg–1·min–1 reaches the pathophysiological range (4, 11). Our measurements of plasma ET-1 are consistent with values reported in human (1, 6, 13, 20, 24) and animal heart failure (3, 22, 25). Our larger dose of ET-1 (4.0 ng·kg–1·min–1) is close to the upper limit of the pathophysiological range of ET-1 plasma levels reported earlier. Thus circulating ET-1 levels within the pathophysiological range reach the threshold for impairing {beta}-adrenergic dilation of resistance coronary vessels.

Our approach involves analyses of relations between CS PO2 or CBF and MO2 to assess the balance between myocardial O2 supply and demand. As expected, graded doses of dobutamine alone increased MO2 secondary to higher cardiac metabolic demand. As MO2 increased, the rise in CBF was accompanied by elevations of CS blood PO2, indicative of a shift in the O2 supply-demand balance. Therefore, the increases in CBF triggered by {beta}-adrenergic receptor activation exceeded cardiac metabolic demand, consistent with a direct coronary dilator process. The positive slope of the relation between CS PO2 and MO2 reflects the magnitude of dilator responses. A perfect match between CBF and cardiac metabolic demand would be translated into a slope of the PO2-MO2 relation close to zero.

In the present study, elevations of circulating ET-1 levels decreased the slope of the relation between CS PO2 or CBF and MO2. As MO2 increased during dobutamine administration, CS PO2 and CBF rose disproportionately less after ET-1 (2.5 or 4.0 ng·kg–1·min–1 iv) than before ET-1. Thus dobutamine-induced coronary dilation was reduced by elevations of circulating levels of ET-1. If ET-1 completely prevented coronary dilation to dobutamine, the slope of the PO2-MO2 relation should become negative, as demonstrated earlier in dogs (17), when CBF is solely driven by cardiac metabolic demand. Consequently, a residual dilator effect of dobutamine remained during ET-1 delivery.

In the present study, we have ensured that plasma ET-1 levels reached a steady state throughout the dobutamine infusions. This makes it unlikely that a growing vasoconstrictor influence of ET-1 accounted for the impaired {beta}-adrenergic coronary dilation reflected by the reduction in the slopes of CS PO2 and CBF vs. MO2 relations. Given that ET-1 lacked significant effects on baseline CBF, CS PO2, and MO2 in the present study, the reduction of {beta}-adrenergic coronary dilation cannot be causally related to a competition with a vasoconstrictor effect of ET-1. The maintained ACh- and NTG-induced dilator responses after ET-1 are consistent with this conclusion.

On the basis of our previous studies showing that blockade of NO formation impairs {beta}-adrenergic dilation of resistance coronary vessels (16), we were led to hypothesize that ET-1 may interfere with NO-dependent dilation, thereby limiting {beta}-adrenergic dilation. Our data with intracoronary administration of ACh and NTG to avoid the confounding influence of changes in hemodynamic variables argue against that possibility, because responses to both agonists were maintained in the face of elevated ET-1 plasma levels. These data also imply that the inhibitory effect of ET-1 on coronary dilation is selectively displayed against {beta}-adrenergic effects and does not extend to other vasodilators, such as ACh and NTG. This rules out the possibility that ET-1 acted as a nonspecific inhibitor of coronary dilation.

Earlier, we demonstrated that opening of KATP channels plays a pivotal role in {beta}-adrenergic dilation of resistance coronary vessels (16). Conceivably, ET-1 may interfere with KATP channels to impair {beta}-adrenergic coronary dilation. Consistent with this hypothesis, patch-clamp experiments on isolated vascular smooth muscle cells indicate that ET-1 blocks KATP channels (18). Furthermore, cromakalim, a KATP channel opener, prevented ET-1-induced constriction of dorsal hand veins in humans (8). If ET-1 interferes with the opening of KATP channels, adenosine-induced dilation, which primarily involves the opening of KATP channels on coronary microvessels (9), should also be impaired. As predicted, ET-1 antagonized CBF responses to intracoronary adenosine to specifically target coronary vessels. To directly demonstrate an inhibitory effect of ET-1 on KATP-dependent responses, the effects of intracoronary lemakalim, a KATP channel opener, were assessed before and during ET-1 delivery. As expected, ET-1 antagonized lemakalim-induced CBF responses. Taken together, the above findings are consistent with the possibility of an inhibitory effect of ET-1 on {beta}-adrenergic dilation of resistance coronary vessels through a KATP channel-dependent process.

In contrast to coronary responses, LV inotropic effects of dobutamine were maintained and even increased during ET-1 delivery. The rise in MAP caused by ET-1 may have influenced LV inotropic responses to dobutamine by increasing baroreflex influences. To assess that possibility, experiments were conducted after ganglionic blockade. In that situation, dobutamine-induced LV dP/dt increases were augmented by ET-1, whereas coronary dilator responses were blunted. The present data are at variance with reports on isolated cardiomyocytes, where exposure to ET-1 prevented isoproterenol-induced cAMP increases (10, 30) and the opening of L-type Ca2+ channels (27, 32), which should impair inotropic responses. Presumably, species differences account for the discrepancy of ET-1 effects on {beta}-adrenergic responses in cardiomyocytes. In myocardial sarcolemmal preparations of ventricular human tissue, ET-1 failed to alter stimulated cAMP production caused by isoproterenol and forskolin (31). ET-1 has been reported to blunt cAMP accumulation in human pericardial smooth muscle cells (34), a finding consistent with our data on vascular responses.

A previous study has examined the effects of elevations of circulating ET-1 levels to the pathophysiological range under baseline conditions in anesthetized dogs (11). A rise in ET-1 created by exogenous ET-1 (2.5 ng·kg–1·min–1) failed to alter baseline CBF in anesthetized dogs. Although the balance between O2 supply and demand was not specifically examined in that study, the present data agree with the conclusion that ET-1 has little influence on baseline CBF. NO and prostacyclin production may counteract ET-1-dependent coronary constriction (12, 29), as suggested earlier.

In the present study, clazosentan failed to alter baseline CS PO2, consistent with limited ET-dependent effects under baseline conditions. In contrast, CS Hb O2 saturation has been reported to increase after ETA or ETA/ETB receptor blockade in earlier studies (15, 26), consistent with significant baseline ET-1-dependent constrictor effects. Our present data also indicate a rise in percent Hb O2 saturation levels (from 18.9 ± 3.6 to 20.7 ± 4.3%, P < 0.05) after clazosentan. This emphasizes the possibility of a discrepancy arising from the use of CS Hb O2 saturation levels as a surrogate for CS PO2.

In the present study, ET receptors accounting for the ET-1-{beta}-adrenergic cross talk were of the ETA subtype. ETA receptor blockade with clazosentan prevented the reduction in slope of the CS PO2-MO2 relation caused by ET-1 given during dobutamine. We previously demonstrated in canine isolated large epicardial coronary arteries that clazosentan (Ro 61-1790) antagonized ET-1-induced contraction through the blockade of ETA receptors (28). In our conscious dogs, systemic clazosentan caused a modest but significant increase in baseline circulating ET-1 levels, presumably as a result of displacement of native ET-1 from its binding sites. It is unlikely that a substantial blockade of ET-1 clearance through ETB receptor blockade was involved, given that acute blockade of ETA/ETB receptors in dogs caused disproportionately greater (10- to 20-fold increase from baseline) increases in circulating ET-1 levels than those observed in the present study (23, 26). In the aggregate, ETA receptors were pivotal in the inhibitory action of ET-1 on {beta}-adrenergic dilation of resistance coronary vessels.

In conclusion, pathophysiological levels of ET-1 substantially impair {beta}-adrenergic dilation of resistance coronary vessels through an ETA receptor-dependent process. In contrast, endothelium-dependent and -independent coronary responses to ACh and NTG were maintained during ET-1 delivery. On the basis of the inhibitory effect of ET-1 on adenosine- and lemakalim-induced dilation, blockade of KATP channels is most likely the mechanism by which ET-1 impairs {beta}-adrenergic coronary dilation. As opposed to the inhibitory effects of ET-1 on vascular {beta}-adrenergic responses, LV inotropic responses to dobutamine were not impaired by ET-1. On a speculative basis, ET-1 receptor blockade may serve as significant adjunct to dobutamine to improve the match between myocardial O2 supply and demand in patients requiring inotropic support.


   GRANTS
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This work was supported through grants from the Canadian Heart and Stroke Foundation, the Canadian Institute for Health Research, and Fonds de Recherche de l'Institut de Cardiologie de Montréal.


   ACKNOWLEDGMENTS
 
The authors are grateful to C. Mousseau and M.-H. Roy for expert technical assistance and Dr. N. Trescases for plasma sample analyses. Clazosentan was generously supplied by Martine Clozel (Actelion Pharmaceuticals).


   FOOTNOTES
 

Address for reprint requests and other correspondence: M. Lavallée, Institut de Cardiologie de Montréal, Centre de Recherche, 5000 Bélanger East, Montréal, Quebec, Canada H1T 1C8 (E-mail: lavallem{at}icm.umontreal.ca)

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
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Aronson D and Burger AJ. Neurohormonal prediction of mortality following admission for decompensated heart failure. Am J Cardiol 91: 245–248, 2003.[CrossRef][ISI][Medline]
  2. Asano K, Bohlmeyer TJ, Westcott JY, Zisman LS, Kinigawa K, Good M, Minobe WA, Roden RL, Wolfel EE, Lindenfeld J, Port JD, Perryman MB, Cleveland 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][ISI][Medline]
  3. Borgeson DD, Grantham JA, Williamson EE, Luchner A, Redfield MM, Opgenorth TJ, and Burnett JC Jr. Chronic oral endothelin type A receptor antagonism in experimental heart failure. Hypertension 31: 766–770, 1998.[Abstract/Free Full Text]
  4. Donckier JE, Hanet C, Berbinschi A, Galanti L, Robert A, Van Mechelen H, Pouleur H, and Ketelslegers JM. Cardiovascular and endocrine effects of endothelin-1 at pathophysiological and pharmacological plasma concentrations in conscious dogs. Circulation 84: 2476–2484, 1991.[Abstract/Free Full Text]
  5. Dupuis J, Cernacek P, Tardif JC, Stewart DJ, Gosselin G, Dyrda I, Bonan R, and Crépeau J. Reduced pulmonary clearance of endothelin-1 in pulmonary hypertension. Am Heart J 135: 614–620, 1998.[CrossRef][ISI][Medline]
  6. Givertz MM, Colucci WS, LeJemtel TH, Gottlieb SF, Hare JM, Slawsky MT, Leier CV, Loh E, Nicklas JM, and Lewis BE. Acute endothelin A receptor blockade causes selective pulmonary dilation in patients with chronic heart failure. Circulation 101: 2922–2927, 2000.[Abstract/Free Full Text]
  7. Gorman MW, Tune JD, Richmond KN, and Feigl EO. Feedforward sympathetic coronary vasodilation in exercising dogs. J Appl Physiol 89: 1892–1902, 2000.[Abstract/Free Full Text]
  8. Haynes WG and Webb DJ. Venoconstriction to endothelin-1 in humans: role of calcium and potassium channels. Am J Physiol Heart Circ Physiol 265: H1676–H1681, 1993.[Abstract/Free Full Text]
  9. Hein TW and Kuo L. cAMP-independent dilation of coronary arterioles to adenosine. Role of nitric oxide, G proteins, and KATP channels. Circ Res 85: 634–642, 1999.[Abstract/Free Full Text]
  10. Jones LG. Inhibition of cyclic AMP accumulation by endothelin is pertussis toxin sensitive and calcium independent in isolated adult feline cardiac myocytes. Life Sci 58: 115–123, 1996.[CrossRef][ISI][Medline]
  11. Lerman A, Hildegrand FL, Aarhus LL, and Burnett JC Jr. Endothelin has biological actions at pathophysiological concentrations. Circulation 81: 1808–1814, 1991.
  12. Lerman A, Sandok EK, Hildebrand FL, and Burnett JC Jr. Inhibition of endothelium-derived relaxing factor enhances endothelin-mediated vasoconstriction. Circulation 85: 1894–1898, 1992.[Abstract/Free Full Text]
  13. Lüscher TF, Enseleit F, Pacher R, Motrovic V, Schulze MR, Willenbrock R, Dietz R, Rousson V, Hürlimann D, Philipp S, Notter T, Noll G, and Ruschitzka R. Hemodynamic and neurohumoral effects of selective endothelin A (ETA) receptor blockade in chronic heart failure. Circulation 106: 2666–2672, 2002.[Abstract/Free Full Text]
  14. Merkus D, Duncker DJ, and Chilian WM. Metabolic regulation of coronary vascular tone: role of endothelin-1. Am J Physiol Heart Circ Physiol 283: H1915–H1921, 2002.[Abstract/Free Full Text]
  15. Merkus D, Houweling B, Mirza A, Boomsma F, van den Meiracker AH, and Duncker DJ. Contribution of endothelin and its receptors to the regulation of vascular tone during exercise is different in the systemic, coronary and pulmonary circulation. Cardiovasc Res 59: 745–754, 2003.[Abstract/Free Full Text]
  16. Ming Z, Parent R, and Lavallée M. {beta}2-Adrenergic dilation of resistance coronary vessels involves KATP channels and nitric oxide in conscious dogs. Circulation 95: 1568–1576, 1997.[Abstract/Free Full Text]
  17. Miyashiro JK and Feigl EO. Feedforward control of coronary blood flow via coronary {beta}-receptor stimulation. Circ Res 73: 252–263, 1993.[Abstract/Free Full Text]
  18. Miyoshi Y, Nakaya Y, Wakatsuki T, Nakaya S, Fujino K, Saito K, and Inoue I. Endothelin blocks ATP-sensitive K+ channels and depolarizes smooth muscle cells of porcine coronary artery. Circ Res 70: 612–616, 1992.[Abstract/Free Full Text]
  19. Pernow J, Kaijser L, Lundberg JM, and Ahlborg G. Comparable potent coronary constrictor effects of endothelin-1 and big endothelin-1 in humans. Circulation 94: 2077–2082, 1996.[Abstract/Free Full Text]
  20. Rousseau MF, Gurné O, Duprez D, Van Mieghem W, Robert A, Aahn S, Galanti L, and Ketelslegers JM. Beneficial neurohormonal profile of spironolactone in severe congestive heart failure. J Am Coll Cardiol 40: 1596–1601, 2002.[Abstract/Free Full Text]
  21. Roux S, Breu V, Giller T, Neidhart W, Ramuz H, Coassolo P, Clozel JP, and Clozel M. Ro 61-1790, a new hydrosoluble endothelin antagonist: general pharmacology and effects on experimental cerebral vasospasm. J Pharmacol Exp Ther 283: 1110–1118, 1997.[Abstract/Free Full Text]
  22. Saad D, Mukherjee R, Thomas PB, Iannini JP, Basler CG, Hebbar OSJ, Moreland S, Webb ML, Powell JR, and Spinale FG. The effects of endothelin-A receptor blockade during the progression of pacing-induced congestive heart failure. J Am Coll Cardiol 32: 1779–1786, 1998.[Abstract/Free Full Text]
  23. Shimoyama H, Sabbah HN, Borzak S, Tanimura M, Shevlyagin S, Scicli G, and Goldstein S. Short-term hemodynamic effects of endothelin receptor blockade in dogs with chronic heart failure. Circulation 94: 779–784, 1996.[Abstract/Free Full Text]
  24. Stangl K, Dschietzig T, Richter C, Laule M, Stangl V, Tanis E, Baumann G, and Felix SB. Pulmonary release and coronary and peripheral consumption of big endothelin and endothelin-1 in severe heart failure. Acute effects of vasodilator therapy. Circulation 102: 1132–1138, 2000.[Abstract/Free Full Text]
  25. Tadano K, Suzuki J, Hanada K, Nakao M, Nakao R, Uehara S, Ohta H, Miyauchi T, and Nishikibe M. Pathophysiological roles of endogenous endothelin-1 in dogs with chronic heart failure produced by rapid right ventricular pacing. J Pharmacol Exp Ther 298: 729–736, 2001.[Abstract/Free Full Text]
  26. Takamura M, Parent R, Cernacek P, and Lavallée M. Influence of dual ETA/ETB-receptor blockade on coronary responses to treadmill exercise in dogs. J Appl Physiol 89: 2041–2048, 2000.[Abstract/Free Full Text]
  27. 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 503: 55–65, 1997.[CrossRef][ISI][Medline]
  28. Thorin E, Parent R, Ming Z, and Lavallée M. Contribution of endogenous endothelin to large epicardial coronary artery tone in dogs and humans. Am J Physiol Heart Circ Physiol 277: H524–H532, 1999.[Abstract/Free Full Text]
  29. Traverse JH, Judd D, and Bache RJ. Dose-dependent effect of endothelin-1 on blood flow to normal and collateral-dependent myocardium. Circulation 93: 558–566, 1996.[Abstract/Free Full Text]
  30. Volgelsang M, Broede-Sitz A, Schafer E, Zerkowski HR, and Brodde OE. Endothelin ETA-receptors couple to inositol phosphate formation and inhibition of adenylate cyclase in human right atrium. J Cardiovasc Pharmacol 23: 344–347, 1994.[ISI][Medline]
  31. Walker CA, Ergul A, Grubbs A, Zile MR, Zellner JL, Crumbley J, and Spinale FG. {beta}-Adrenergic and endothelin receptor interaction on dilated human cardiomyopathic myocardium. J Card Fail 7: 129–137, 2001.[CrossRef][ISI][Medline]
  32. Watanabe T and Endoh M. Characterization of the endothelin-1-induced regulation of L-type Ca2+ current in rabbit ventricular myocytes. Naunyn Schmiedebergs Arch Pharmacol 360: 654–664, 1999.[CrossRef][ISI][Medline]
  33. Williamson DJ, Wallman LL, Jones R, Keogh AM, Scroope F, Penny R, Weber C, and Macdonald PS. Hemodynamic effects of bosentan an endothelin receptor antagonist, in patients with pulmonary hypertension. Circulation 102: 411–418, 2000.[Abstract/Free Full Text]
  34. Wu-Wong JR and Opgenorth TJ. Endothelin and isoproterenol counter-regulate cAMP and mitogen-activated protein kinases. J Cardiovasc Pharmacol 31 Suppl 1: S185–S191, 1998.




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
287/4/H1476    most recent
00297.2004v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Okajima, M.
Right arrow Articles by Lavallée, M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Okajima, M.
Right arrow Articles by Lavallée, M.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online
Copyright © 2004 by the American Physiological Society.