RHC 3659: a new orally active angiotensin converting enzyme inhibitor in normal volunteers

1 The new converting enzyme inhibitor RHC 3659 was tested in 15 male volunteers. The study consisted of two parts: first, the ability of a single oral dose (5, 10, 20, 40 or 80 mg) to inhibit the pressor response to exogenous angiotensin I was tested with blood pressure and heart rate monitored continuously through an intraarterial catheter. A dose-related shift to the right of the pressor response curve to angiotensin I was observed with a peak occurring within 0.5 to 1 h. The pressor response to angiotensin II was unaffected. 2 In the second part, plasma renin and converting enzyme activity, angiotensin II and aldosterone were measured serially before and up to 8 h after administration of a single oral dose of RHC 3659. As expected. plasma angiotensin II and aldosterone fell within 30 min while plasma renin activity increased. Plasma converting enzyme activity was suppressed at 0.5 h in a dose-related manner with levels still below 30% of control 4 h following 80 mg of the inhibitor. 3 However, in vitro the enzyme-inhibitor complex seemed quited fragile since during storage of the plasma samples at -20 degrees C, converting enzyme activity increased significantly already within days (P less than 0.001, n = 28) and continued to rise for more than 2 months. This fragility may explain the seemingly lower potency of RHC 3659 when compared to captopril. No side effects were observed.

Three new long-acting converting-enzyme inhibitors: relationship between plasma converting-enzyme activity and response to angiotensin I

Three new angiotensin converting-enzyme inhibitors were given orally to 20 men in single doses ranging from 1.25 to 40 mg. Two of them induced comparable marked inhibition of both the blood pressure response to exogenous angiotensin I and plasma converting-enzyme activity. Onset of action was relatively slow, but 21 to 24 hr after drug plasma converting-enzyme activity was still clearly reduced. The third was less active. There was a close correlation between blood pressure response on administration of angiotensin I and plasma converting-enzyme activity. There were no adverse effects. These new drugs are interesting because of their long duration of action. The measurement of plasma converting-enzyme activity seems useful for monitoring efficacy of converting-enzyme blockade and compliance to therapy.