ALPHA-2-ADRENOCEPTOR-MEDIATED ANTISECRETORY EFFECT OF HYPOXIA IN CONSCIOUS RATS

Gastric acid secretion is suppressed, resulting in a significant rise in gastric pH, when conscious rats are exposed to hypoxia (Yamaji et a l., 1996). When adrenal medullectomized rats were exposed to moderate (10.5% O-2) hypoxia for 3 h, gastric acid secretion was restored to ne arly the level in normoxia by the adrenal medullectomy. In severe (7.6 % O-2) hypoxia, the operation also caused an increase in the level of gastric acid output, although the extent was lower than that under 10. 5% O-2 hypoxic conditions. Gastric pH was normalized by the operation even with 7.6% O-2 hypoxia. Similar results were obtained when reserpi ne, which causes an adrenergic discharge, was administered, When an al pha 2-adrenoceptor blocking agent, yohimbine, was administered, the in hibitors-effect of 10.5% and 7.6% O-2 hypoxia on gastric acid secretio n was almost completely removed. However, neither prazosin (an alpha 1 -adrenoceptctr blocker) nor propranolol (a beta-adrenoceptor blocker) showed any significant effects on gastric acid output in hypoxia. Thes e results indicate that acute hypoxia stimulated the adrenergic respon se from the adrenal medulla, and that gastric acid secretion was conse quently suppressed through alpha 2-adrenoceptor.