INVESTIGATIONS ON THE POSSIBLE INVOLVEMENT OF BRADYKININ IN THE ACUTEREGULATION OF THE SECRETION FROM RAT ADRENAL-CORTEX

The presence of an intra-adrenal kallikrein-kinin system suggests the possible involvement of bradykinin (BK) in the regulation of adrenal f unctions. The present study aimed at invetigating whether BK is involv ed in the in vivo acute regulation of aldosterone (ALDO) and corticost erone (B) secretions in the rat. The bolus subcutaneous administration of 4 nmol of BK markedly raised the plasma concentrations of ALDO (PA C) and B (PBC) 60 min after the injection; PAC and PBC returned to the baseline within 120 min. D-Arg, [Hyp(3), D-Phe(7)]-BK, a specific ant agonist of BK receptors (BK-A) did not suppress BK effects, and unexpe ctedly increased PAC and PBC and potentiated the secretagogue action o f BK. BK was found to elicit a net rise in PAC and PBC also in rats be aring enucleated-regenerated adrenal glands deprived of medullary chro maffin cells. In light of the present findings the hypothesis is advan ced that BK plays a role in the acute regulation of secretion of the a drenal cortex in rats, probably by a receptor-independent mechanism, w hose elucidation requires further studies, but which does not conceiva bly involve cortical-medullary paracrine interactions. The marked secr etagogue effect of BK-A may be ascribed to its hypertensive action, wh ich by increasing adrenal blood flow raises steroid release.