Role of vasopressin in stimulation of ACTH secretion by angiotensin II in conscious dogs.

Three series of experiments were performed in conscious dogs to test the possibility that the stimulation of adrenocorticotropin (ACTH) release by angiotensin II (ANG II) is mediated by arginine vasopressin (AVP). In the first protocol, the effect of ANG II on ACTH release was studied in dogs in which endogenous AVP levels had been increased by water deprivation. Water deprivation for 24 h increased plasma AVP concentration from 3.0 +/- 0.5 to 7.7 +/- 0.5 pg/ml (P less than 0.01) and increased the AVP response to the highest dose of ANG II (20 ng X kg-1 X min-1). Despite these changes, water deprivation failed to increase the ACTH response to ANG II. Next, the contribution of endogenous AVP to the stimulation of ACTH release by ANG II was examined using the V1-receptor antagonist, d(CH2)5Tyr[Met]-AVP (10 micrograms/kg iv). The ACTH response to ANG II in the presence of the AVP antagonist (66.4 +/- 3.1 to 100.1 +/- 15.9 pg/ml) was not significantly less than that in its absence (53.0 +/- 4.8 to 72.2 +/- 11.1 pg/ml). Finally, ANG II and AVP were infused in combination to determine whether there is a synergism between these two peptides in the release of ACTH. In one protocol, AVP and ANG II were infused separately and in combination. The ACTH response to ANG II and AVP in combination (48.7 +/- 6.5 to 61.5 +/- 8.5 pg/ml) was not enhanced compared with the responses to ANG II (59.8 +/- 7.3 to 71.0 +/- 10.1 pg/ml) or AVP (48.8 +/- 5.7 to 55.6 +/- 6.5 pg/ml) alone.(ABSTRACT TRUNCATED AT 250 WORDS)