Modulation of systolic and diastolic function by endothelin-1: relation to coronary flow

ET-1 increases distensibility of acutely loaded myocardium: a novel ETA and Na+/H+ exchanger-mediated effect

This study investigated, in rabbit papillary muscles (n = 61) and human auricular strips (n = 7), effects of endothelin-1 (ET-1; 0.1-10 nM) on diastolic myocardial properties. ET-1 (1 nM) was also given in the presence of selective ET(A) or ET(B) antagonism, nonselective ET(A)/ET(B) antagonism, and Na(+)/H(+) exchanger inhibition. Effects of 6.3 mM Ca(2+) were also studied. ET-1 dose dependently increased inotropism. In contrast to baseline, in the presence of ET-1, resting tension (RT) decreased, after an isometric twitch, 3.4 +/- 1.4, 6.9 +/- 1.5, and 12.5 +/- 3.1% with 0.1, 1, and 10 nM, respectively, reflecting an increase in myocardial distensibility. ET-1 effects were abolished with selective ET(A) as well as with nonselective ET(A)/ET(B) antagonism, whereas they were still present with ET(B) antagonism. Na(+)/H(+) exchanger inhibition abolished ET-1 effects on distensibility, whereas it only partially inhibited positive inotropic effect. Ca(2+) increased inotropism to a similar extent to ET-1 (1 nM) but did not affect distensibility. ET-1 therefore increased diastolic distensibility of acutely loaded human and nonhuman myocardium. This effect is mediated by ET(A) receptors, requires Na(+)/H(+) exchanger activation, and cannot be elicited by Ca(2+).

Role of endothelin-1 receptors in healthy anaesthetized rabbits

1. Many diseases are associated with elevated endothelin (ET)-1 plasma concentrations. In order to understand the consequence of this elevation, in the present study the effects of exogenous ET-1 on the entire organsim were investigated, in particular with respect to the role of ETA and ETB receptors in the cardiovascular system. In open-chest rabbits, left ventricular (LV) pressure (LVPmax, LVPed), dP/dtmax and dP/dtmin were recorded in ejecting and isovolumically beating hearts to determine cardiac function. In addition, heart rate (HR), aortic pressure (AoP) and aortic flow (AoF) were measured. Total peripheral resistance (TPR) was calculated from mean AoP and AoF. 2. In the first series of experiments (n = 11), ET-1 (0.5 nmol/kg; bolus) produced a non-significant reduction in HR. Systolic function, in terms of AoF, LVPmax and dP/dtmax, was improved; for example, LVPmax was increased significantly (69 +/- 10 vs 106 +/- 20 mmHg for control and ET-1, respectively; P < 0.05). Similarly, early relaxation (dP/dtmin) was improved. In parallel, TPR rose significantly (0.25+/-0.07 vs 0.35+/-0.1 mmHg/min per mL for control and ET-1, respectively; P < 0.05). Isovolumic measurements showed corresponding responses. 3. In the second series of experiments (n = 7), animals were pretreated with an ETA receptor antagonist (330 nmol/min per kg FR 139317). After ETA receptor blockade, the administration of ET-1 had no significant effect on cardiac function or vasomotion. 4. In the third series of experiments (n = 6), animals were pretreated with an ETB receptor antagonist (10 nmol/min per kg BQ 788). In this series of experiments, the effects of ET-1 on cardiac function and vasomotion were the same as in the first series of experiments, except for the effect on HR, which decreased by 35% after ET-1. 5. In our experimental model, exogenous ET-1 exerted a clear-cut positive inotropic effect, together with the anticipated peripheral vasoconstriction via ETA receptors.

Calcium handling and role of endothelin-1 in monocrotaline right ventricular hypertrophy of the rat

We investigated the role of endothelin-1 (ET-1) in right ventricular function and intracellular Ca(2+)(Ca(2+)(i)) handling of isolated perfused rat hearts with right ventricular hypertrophy induced by monocrotaline (50 mg/kg). Nine weeks after monocrotaline (n=9) or saline (control n=9) treatment, hearts were perfused isovolumically at 37 degrees C and right ventricular function (fluid-filled balloon), right ventricular intracellular Ca(2+) transients (aequorin bioluminescence method) and the effects of ET-1 were determined. Monocrotaline-treated rats developed considerable right ventricular hypertrophy (right ventricular weight:body weight ratio: 1.07+/-0.13 v. 0.60+/-0.03 in controls P<0.05) and these hearts generated higher right ventricular systolic and diastolic pressure, but similar systolic and diastolic wall stress, indicating a compensated functional state. Hypertrophied hearts demonstrated a prolonged duration of isovolumic contraction (time to 90% decline from peak: 105+/-1 v 89+/-4 ms at 3 m M extracellular Ca(2+) P<0.05), but neither the time to peak pressure (71+/-3 ms) nor time to peak light (25+/-3 ms) were different from controls. The increased duration of contraction correlated with a similar prolongation of the Ca(2+)transient (time to 90% decline from peak: 72+/-4 v 50+/-3 ms P<0.05), indicating a reduced rate of Ca(2+)sequestration in hypertrophic right ventricles. Peak systolic intracellular Ca(2+)was similar in control and hypertrophied hearts (1.04+/-0.02 and 0.99+/-0.02 microM, P>0.05, n=6). ET-1 (1-300 p M) affected neither the time course of right ventricular contraction nor that of the Ca(2+)transient or peak systolic Ca(2+)concentrations. These data are the first measurements of right ventricular Ca(2+)transients in beating normal and hypertrophic hearts. We conclude that ET-1 plays no role in compensated hypertrophy because it affected neither right ventricular function nor intracellular Ca(2+)handling in this model.

Endothelin-1 receptor antagonism does not influence myocardial function in hypertensive dogs

BACKGROUND

As endothelin-1 exerts positive inotropic effects, the present study evaluated whether the hypotensive effects of the endothelin-1 receptor antagonist bosentan were partially related to a decrease in myocardial performance.

METHODS

In group I, eight anaesthetized open-chest dogs with perinephritic hypertension received four cumulative doses of bosentan (B1-B4). In group II, eight animals received the same doses of bosentan after autonomic blockade. Indices of heart function were derived from the pressure-length loops obtained during vena cava occlusion.

RESULTS

In group I, bosentan decreased left ventricular systolic pressure (LVSP) and mean aortic pressure (MAP) dose dependently, reaching 21% and 23% respectively at B4 (LVSP from 190 +/- 8 to 150 +/- 5 mmHg, P < 0.001; MAP from 167 +/- 7 to 128 +/- 5 mmHg, P < 0.001). These effects were only related to peripheral vasodilatation, without depression of myocardial contractility, as systemic vascular resistance dropped (from 670 +/- 83 to 446 +/- 53 mmHg mL-1 min-1 x 10(4); P < 0.05), and the end-systolic pressure-length relationship (ESPLR) remained unchanged (4.0 +/- 0.4 vs. 4.3 +/- 0.7 mmHg mm-1 kg-1). Concomitantly with pressure decline, heart rate tended to increase in this group (from 150 +/- 4 to 156 +/- 6 beats min-1). When autonomic system was blocked (group II), administration of bosentan induced similar hypotensive effects as in group I (26% and 28% reduction in LVSP and MAP respectively, P < 0.001) whereas ESPLR did not change (3.0 +/- 0.9 vs. 3.1 +/- 0.5mmHg-1 mm kg-1 ). Under these sympathetically blocked conditions, heart rate significantly fell after bosentan infusion (from 120 +/- 4 to 110 +/- 6 beats min-1, P < 0.001).

CONCLUSIONS

Without influencing heart function, bosentan is an efficient and safe therapy that opens up new therapeutic perspectives in human essential hypertension.

Inhibition of granulocyte-derived proteases reduces the increase in plasma endothelin associated with myocardial ischemia in the pig

Plasma endothelin (ET) is increased in association with myocardial infarction. The aim of the present study was to get insight into the mechanisms behind this ischemia-induced increase in plasma ET. Since granulocytes increase ET production in vitro, we examined to what extent inhibition of granulocyte-derived proteases could reduce the increase in plasma ET observed in association with myocardial ischemia. We infused Eglin C, a selective inhibitor of the granulocyte-derived proteases elastase, cathepsin G, and chymotrypsin, in pigs subjected to 90 min left anterior descending coronary artery occlusion followed by 210 min reperfusion (n = 7). Arterial plasma ET increased in an untreated control group (n = 7) from 5.0 +/- 0.6 (mean +/- SEM) fmol . ml-1 before myocardial ischemia to 6.1 +/- 0.6 fmol . ml. at 90 min ischemia and reached a maximum of 6.8 +/- 0.9 fmol . ml-1 at 90 min reperfusion. The increase in plasma ET associated with myocardial ischemia was almost completely abolished in the Eglin C treated group (p = 0.005). Plasma ET in the Eglin C treated animals was 4.7 +/- 0.4, 4.7 +/- 0.4, and 4.6 +/- 0.4 fmol . ml-1 before myocardial ischemia, at 90 min ischemia, and at 90 min reperfusion, respectively. Our study suggests a role for granulocyte-derived proteases in the increase in plasma ET associated with myocardial ischemia. We have shown that the increase in plasma ET associated with myocardial ischemia was reduced by inhibition of granulocyte-derived proteases using the selective protease inhibitor Eglin C.