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

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Abstract
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)

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