Enhancement of angiotensin-converting enzyme activity in the inner cortex of rat kidney by captopril

The rat kidney was separated into the outer cortex, inner cortex, outer medulla and inner medulla or papilla, and the distribution of angiotensin-converting enzyme (ACE) in response to consecutive administrations of captopril was studied. In normal animals, the ACE activity in the inner cortex and outer medulla was about 10 and 3 times higher than in the outer cortex, respectively, and the activity in the inner medulla was much the same as that in the outer cortex. Captopril was given in doses of 30 and 100 mg/kg/day for 7 days, and the renal ACE activity on the 8th day was examined. Since it was assumed that the ACE activity might be lower than the full activity when the tissue contained captopril, diamide, a sulfhydryl oxidant, was used to eliminate the effect of any captopril remaining in the tissue extracts. However, this compound at concentrations over 1 mM enhanced the activity of ACE itself to about twice the value when assayed without diamide. Thus, oxidation with sufficient concentrations of diamide resulted in an enhancement of a maximal activity of ACE. When all samples were pretreated with 10 mM diamide and the ACE activity determined, captopril caused a dose-related increase in the ACE activity, but only in the inner cortex. We conclude that ACE locates predominantly in the inner cortex of the rat kidney and it is this area which has an altered ACE activity in response to captopril.