Vasoactivity of adrenaline in regions covering the canine gastrointestinal tract

Little is known about the action adrenaline has on vascular areas of functionally different parts of the stomach and intestine. Therefore the vasoactivity of adrenaline (1-1024 ng/kg i.v.) was studied by electromagnetic flow measurements in 8 vascular beds covering the gastrointestinal tract. Adrenaline induced 1) a vasodilation in the lesser curvature and antrum of the stomach; 2) a vasoconstriction in the greater curvature of the stomach; 3) a vasoconstriction followed by a vasodilation in the duodenum and jejunum; 4) a vasoconstriction in the ileum, caecum/colon and colon/rectum. Phenoxybenzamine (750 micrograms/kg i.v.) blocked systematically the vasoconstriction in the duodenum and jejunum but not in the ileum and colon. Vasodilation could be blocked by propranolol (100 micrograms/kg i.v.). It is concluded that 1) adrenaline-effects are mediated predominantly by beta-receptors in the antrum and lesser curvature of the stomach; predominantly by alpha-receptors in the greater curvature of the stomach; by alpha- and beta-receptors in the duodenum and jejunum; 2) receptors in the large intestine are of another alpha-adrenergic type than those in the small intestines. Evidence was provided for a gradient of diminishing vasodilating effects of adrenaline from cranial to caudal of the gut.