EFFECTS OF SUBSTANCE-P ON ADRENAL RESPONSES TO ACETYLCHOLINE IN CONSCIOUS CALVES

The effect of intra-aortic infusions of substance P (SP; 10 or 20 pmol .min(-1).kg(-1)) on adrenal responses to acetylcholine (4.5 nmol.min(- 1).kg(-1) ia) have been investigated in functionally hypophysectomized calves given exogenous adrenocorticotropic hormone (0.7 pmol.min(-1). kg(-1)). At the lower dose, SP had no effect on cortisol output. In co ntrast, SP inhibited the output of both catecholamines and enkephalins in response to acetylcholine, without affecting the output of cortico tropin-releasing factor (CRF). Increasing the dose of SP to 20 pmol.mi n(-1).kg(-1) ia significantly reduced the outputs of both cortisol and CRF (P < 0.025 and 0.01 respectively). It is concluded that SP is cap able of modulating both adrenal cortical and medullary responses to ac etylcholine and that the tatter are more sensitive to this influence t han the former.