EFFECT OF ACETYLCHOLINE INFUSION ON ADRENAL VASCULATURE AND CATECHOLAMINE SECRETION

To evaluate effects of cholinergic receptor stimulation on regional ad renal blood flow (Q, radiolabeled microspheres) and catecholamine secr etion, acetylcholine (ACh) was infused into pentobarbital-anesthetized , ventilated dogs. Unilateral adrenal denervation and placement of lum boadrenal catheters preceded intra-aortic infusion of 1) ACh alone (n = 6), 2) ACh plus hexamethonium (Hex) 20 mg/kg (n = 6), or 3) ACh plus atropine (Atr) (0.5 mg/kg) and Hex. ACh alone and in combination with Hex elicited similar dose-related (2, 20, and 100 mumol/min) increase s in catecholamine secretion (181 +/- 61 to 1,055 +/- 229, 31,644 +/- 9,411, and 179,181 +/- 69,659 ng.min-1.g medulla-1), whereas Hex and A tr together inhibited ACh-induced secretion by 95%. ACh caused marked medullary vasodilation (0.71 +/- 0.05 to 0.14 +/- 0.03 mmHg.ml-1.min.1 00 g) in all three groups. To determine whether medullary vasodilation was due to incomplete muscarinic blockade, Hex-pretreated animals (n = 4) received ACh (100 mumol/min) and three increasing doses of Atr (0 .5, 5, and 25 mg/kg). Catecholamine secretion was inhibited by all dos es of Atr; however, vasodilation was blocked only by the two higher do ses of Atr. These data suggest possible different mechanisms of muscar inic receptor-mediated catecholamine secretion and vasodilation.