The effects of converting enzyme inhibitors on plasma angiotensinogen and plasma aldosterone in sodium-depleted rats.

Plasma angiotensinogen was measured by two different methods in three groups of sodium-depleted rats: control rats, captopril-treated rats and enalapril-treated rats. The enzymatic method of measurement is an exhaustion technique which measures the amount of angiotensin I liberated from plasma by an excess of renin. Direct radioimmunoassay measures both angiotensinogen and its inactive residue, des-angio I-angiotensinogen, and the difference between the results of both methods can be used as an indirect measurement of plasma des-angio I-angiotensinogen. Both converting enzyme inhibitors decreased blood pressure, stimulated renin secretion, decreased plasma angiotensinogen and increased des-angio I-angiotensinogen. Plasma des-angio I-angiotensinogen levels were positively correlated with plasma renin levels. In converting enzyme inhibitor-treated rats, plasma aldosterone was slightly, but not significantly, lower than in control rats. Although plasma aldosterone was significantly correlated with plasma renin both in control rats and converting enzyme inhibitor-treated rats, plasma renin was elevated 10-fold in treated rats.