Bradykinin and pituitary-adrenocortical function in the rabbit: In vitro and in vivo studies

Bradykinin (BK) is a 9-amino acid peptide, which has been found to affect a drenocortical secretion in the calf and rat. We investigated the in vitro a nd in vivo effects of BK and its receptor antagonist [D-Arg, (Hyp(3),D-Phe( 7))]-BK (BK-A) on pituitary-adrenocortical function in the rabbit. BK and B K-A raised basal release of aldosterone, but not of corticosterone by dispe rsed zona glomeralosa and zona fasciculata-reficularis cells, respectively. Both peptides did not affect ACTH-stimulated aldosterone secretion. Conver sely, BK concentration-dependently decreased ACTH-stimulated corticosterone production, and BK-A annulled this effect. The bolus intravenous injection of BK did not alter plasma ACTH concentration. However, BK lowered the blo od concentration of both aldosterone and corticosterone, as well as the ove rall production of the two hormones over a period of 90 min after its admin istration. The simultaneous injection of BK-A blocked these effects of BK. BK-A alone did not evoke any sizeable change in blood hormonal levels. Coll ectively, these findings allow us to conclude that in rabbits (i) exogenous BK depresses adrenocortical secretion, through a receptor-mediated mechani sm, which does not involve the inhibition of pituitary ACTH release-, and ( ii) endogenous BK-like peptides do not play a relevant role in the function al regulation of the pituitary-adrenal axis, at least under basal condition s.