In vitro stability of the inhibition of serum converting enzyme by fosinopril

Interruption of prolonged ramipril treatment in hypertensive patients: effects on the renin-angiotensin system

The increase in renin secretion and the induction of the converting enzyme (ACE) observed during treatment by ACE inhibitors (CEIs) could result in increased angiotensin II (ang II) synthesis when the treatment is stopped. The object of this study was to compare changes in the components of the renin-angiotensin system with changes in arterial pressure in hypertensives, following the cessation of long-term ramipril treatment. Twenty hypertensives, treated for at least three months with ramipril, in monotherapy for the last three weeks, were randomly allocated to two parallel groups and received for fifteen days, on a double-bind basis, either a placebo (withdrawal group W, n = 12) or ramipril at the previous doses (treated group T, n = 8). Blood pressure was measured using four different techniques. The active renin (AR), angiotensinogen, angiotensin I (ang I), angiotensin II (ang II) and aldosterone plasma concentrations were measured, as was plasma angiotensin I converting enzyme (ACE) activity in vitro (colorimetric and fluorimetric method) and in vivo (the ang II/ang I ratio). The biological effects of cessation of long-term ramipril treatment in hypertensives were a decline in AR and angiotensin I concentrations, an increase in ACE activity and no significant changes in angiotensinogen, angiotensin II and aldosterone levels. Fifteen days after withdrawal, the different parameters of the renin-angiotensin system appear to have returned to basal value. A slow rise in blood pressure was also observed but no rebound increase was noted during the 15 days neither in angiotensin II levels nor in blood pressure. Following the cessation of prolonged ramipril treatment, in vivo converting enzyme inhibition disappears slowly, probably on account of the slow tight binding inhibitor properties of ramiprilat, the active metabolite of this CEI. The gradual decline in AF, plasma levels, together with the prolonged ACE inhibition as measured in vivo by the ang II/ang I ratio, explains the absence of a rise in ang II synthesis.