Effect of enalapril on the inotropic response to isoproterenol in renal hypertensive rats.

It is not clear whether regression of cardiac hypertrophy normalizes cardiac contractility. We studied the effect of enalapril treatment on the contractile response to beta-adrenergic stimulation with isoproterenol in renal hypertension. Male Wistar rats (n = 28) were divided into a clipped group (n = 14) and control group (n = 14). Three weeks after surgery, half of the animals from each group received for 21 days either enalapril (2.5 mg/kg) twice a day or vehicle by gastric intubation. Arterial pressure and body weight were measured twice a week. At the end of the experimental period, the hearts were excised, the ventricles were weighed, and the left ventricular papillary muscle was mounted in a bath. Myocardial contractility was characterized by the maximal developed tension, the maximal rate of rise of tension (+T), and the maximal velocity of relaxation (-T), which were measured at basal conditions and after cumulative doses of isoproterenol (10(-11) to 10(-4) M). The ratio of ventricular weight to body weight increased in hypertensive rats. Enalapril induced a decrease in arterial pressure and in the cardiac mass in both treated groups (p less than 0.05). The basal values of maximal developed tension, +T, and -T were similar in the four groups. The increment in +T and -T in response to isoproterenol (10(-4) M) was depressed in the hypertensive animals and in both treated groups (p less than 0.05). There was no significant difference in the +T/-T ratio or in the ED50 among the groups.(ABSTRACT TRUNCATED AT 250 WORDS)