The possible role of endogenous bradykinin in the regulation of the response of rat pituitary-adrenocortical axis to stresses

The role played by endogenous bradykinin (BK) on the hypothalamo -pituitary-adrenal (HPA) axis was investigated in the rat. Normal and ether-stressed (2 min ether-vapor inhalation) or cold-stressed (20 min at 4°C) animals were given a bolus subcutaneous injection of 20 nmol of D-Arg,[Hyp 3, D-Phe 7]-BK, an antagonist of B 2 subtype of BK receptors (BKA); the blood concentrations of ACTH, aldosterone (ALDO) and corticosterone (B) were measured by specific RIA, 1, 2 or 4h after the injection. BKA did not evoke significant changes in the basal plasma levels of the three hormones. Ether and cold stresses notably raised the blood concentrations of ACTH, ALDO and B, being maximal responses observed after 1 or 2h. BKA markedly enhanced the responses of ACTH and B, but not that of ALDO to ether stress. BKA magnified ALDO and B responses to cold stress, but it strikingly depressed ACTH one. In light of these findings, it may be concluded that (i) endogenous BK does not affect basal activity of rat HPA axis, but it exerts a general inhibitory action on its response to the stresses; and (ii) different mechanisms are involved in the cold and ether stress-induced activation of the HPA axis, which could explain the quantitative and qualitative differences observed in the inhibitory action of endogenous BK according to the kind of stress employed.