Effect of Captopril and Aprotinin on Inactive Renin

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Abstract
Inactive renin (prorenin) was measured in plasma from untreated hypertensive patients after acute (60 min) administration of the angiotensin I converting enzyme inhibitor captopril, after 4 wk of treatment with captopril, and after an acute infusion of the protease inhibitor aprotinin. Inactive renin was unchanged during acute captopril therapy despite a 4-fold increase in active renin. After 4 wk of treatment with captopril, inactive renin had increased 2-fold and active renin was also elevated, but to a greater degree (6-fold). Active renin was significantly suppressed by the aprotinin infusion, to about 25%, but the inactive plasma renin level was apparently unchanged. The time course of the responses of active and inactive plasma renins are different; the inactive renin level seems to change more slowly than does active renin in response to the same stimulus. A neutral serine protease inhibitor can rapidly reduce the circulating level of active renin. This observation is consistent with the possibility, but does not prove it, that a kallikrein-like enzyme normally activating prorenin was inhibited by aprotinin.