Influence of converting enzyme inhibition on the release of vasopressin induced by angiotensin.

1 The effects of intravenous infusion of angiotensin I, II and (des-1-Asp) angiotensin II (angiotensin III) on the plasma vasopressin levels, with and without converting enzyme inhibition, were investigated in conscious rats by use of a specific radioimmunoassay. 2 All three peptides caused a dose-dependent increase in vasopressin release, angiotensin III infusion being less effective than angiotensin I or II. 3 The converting enzyme inhibitor, SQ 20881 (Pyr-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro) (1.0 mg/kg, i.v.), had no effect on the plasma vasopressin concentrations in bilaterally nephrectomized rats, but increased them in intact or sham-operated animals. 4 SQ 20881 potentiated vasopressin release, elicited by angiotensin I, leaving that elicited by angiotensin II unchanged. The receptor antagonist, saralasin, prevented the angiotensin-induced increase in plasma vasopressin concentration, even after pretreatment with SQ 20881. 5 These data support the assumption that the renin-angiotensin system may be involved in the control of vasopressin release, and indicate that in addition to angiotensin II, angiotensin I and III may also contribute, acting in concert.