The effects of captopril on rat aortic angiotensin-converting enzyme.

Angiotensin -converting enzyme (ACE) activity was found to be present within the rat aorta using radioenzymatic techniques. Forty-two percent of the enzyme activity was localized within the tunica media. Using an equilibrium dialysis cell system that insured equal free captopril concentrations in both plasma and aorta, converting enzyme in both tissues was observed to possess similar dissociation constants for the inhibitor. Four daily intraperitoneal doses, but not a single dose, of captopril led to a persistent inhibition of aortic-converting enzyme 24 h after final drug administration. Plasma-converting enzyme activity was changed at this time. These results suggest that different pools of converting enzyme recover form captopril inhibition at different rates. The prolonged inhibition of aortic ACE is discussed in terms of drug accumulation within the vessel wall, and the effect of such accumulation on the persistent antihypertensive actions of captopril are also discussed.