Adrenal cortical responses to vasoactive intestinal peptide in conscious hypophysectomized calves

1. Right adrenal and various cardiovascular responses to an intra-aortic infusion of vasoactive intestinal polypeptide (VIP; 4 micrograms min-1 kg-1) have been investigated in the presence and absence of exogenous adrenocorticotrophin, (ACTH1-24; 5 ng min-1 kg-1, i.v.). The adrenal clamp technique was employed in conscious calves in which the pituitary stalk had been cauterized 3-4 days previously. 2. The i.v. infusion of ACTH1-24 increased mean plasma ACTH concentration by between 1000 and 1100 pg ml-1 and mean right cortisol output by about 700 ng min-1 kg-1. Under these conditions the intra-aortic infusion of VIP produced a further rise in mean adrenal cortisol output, together with a consequential rise in mean arterial plasma cortisol concentration, without affecting the concentration of ACTH in the arterial plasma significantly. In the absence of ACTH the same infusion of VIP had no detectable effect on adrenal cortisol output. 3. In each of the above respects this intra-aortic infusion of VIP closely mimicked the effect of stimulation of the peripheral end of the right splanchnic nerve in these animals, as it also did by causing a substantial fall in adrenal vascular resistance in the absence, but not in the presence, of ACTH. 4. It is concluded that release of this peptide from splanchnic nerve terminals in the adrenal gland most probably accounts, at least in part, for the powerful adrenocortical steroidogenic response to splanchnic nerve stimulation, that occurs in the presence of submaximal doses of ACTH.