INVESTIGATIONS ON THE ACUTE EFFECTS OF NEUROPEPTIDES ON THE PITUITARY-ADRENOCORTICAL FUNCTION IN NORMAL AND COLD-STRESSED RATS .1. BOMBESIN AND NEUROMEDIN-B

The effects of a subcutaneous bolus injection of 2 mu g bombesin (BM) or neuromedin B (NMB) on the function of the hypothalamo-pituitary-adrenocortical (HPA) axis were investigated in both normal and cold-stressed rats. The blood concentrations of ACTH, corticosterone (B) and aldosterone (ALDO) were measured by specific radioimmunoassays 1, 2 or 4 h after the neuropeptide administration. Cold stress strikingly enhanced plasma levels of ACTH, B and ALDO, and these rises lasted unchanged until 4 h. BM and NMB significantly elevated plasma concentrations of ACTH and B in both normal and stressed animals. In both groups of rats the level of circulating ALDO was not apparently affected by neuropeptides. In light of these findings the following conclusions can be drawn: (i) BM and NMB acutely activate the HPA axis, probably by acting via the same receptor; (ii) the mechanism underlying this effect of BM and NMB is independent of that involved in the cold stress-induced activation of the HPA axis; and (iii) the well-known acute ALDO secretagogue effect of ACTH is probably counteracted by a direct inhibitory action of BM and NMB on adrenal zona glomerulosa.