Chronic effects of an orally active selective endothelin-B-receptor antagonist in experimental congestive heart...

Endothelin-B- (ETB) receptors located in vascular beds mainly mediate vasorelaxation, however, long-term treatment with a mixed ETA/ETB receptor antagonist has been shown to improve the survival rate of rats with heart failure in a similar way to ETA-receptor inhibitors. The inhibition of ETB-receptor-mediated action should therefore be beneficial in preventing the deterioration seen in heart failure, despite various adverse hemodynamic effects. We administered K-8794 (Kowa Co. Ltd, Japan, 2mg/kg/day, n = 6), an orally active selective ETB-receptor antagonist, to dogs with heart failure induced by rapid right ventricular pacing for 14 days, commencing 8 days after pacing. Control dogs were given a placebo (n = 6). Mean arterial pressure decreased and systemic vascular resistance increased in both groups at the end of the protocol. In the K-8794 group, however, those values were higher than in the control group. Cardiac output decreased in both groups, but there were no significant differences observed between the two groups. Plasma renin activity and aldosterone increased in both groups at the end of the protocol, however levels in the K-8794 group were significantly lower than those in the control group. In the K-8794 group, it was quite interesting to note that Na excretion and urine flow rate were higher than in the control group. Our findings thus suggest that, although ETB-receptor antagonism produces some hemodynamic disadvantages, it can successfully prevent body fluid retention through the suppression the activation the renin-angiotensin-aldosterone system in dogs with heart failure.