Physiological control of splanchnic blood flow by adrenaline: studies during acute hypoglycaemia in man

Superior mesenteric artery blood flow (SMABF) increases significantly durin g and after the hypoglycaemia reaction in healthy humans. To investigate th e mechanisms controlling this phenomenon, SMABF and plasma catecholamines w ere measured in healthy human volunteers. In 10 controls, hypoglycaemia was induced by insulin infusion (2.5 m-units min(-1).kg(-1)). In six subjects, beta-blockade by propranolol infusion (0.7 mu g min(-1).kg(-1)) preceded i nsulin infusion and was continued throughout the study. Following the hypog lycaemia reaction, the glucose nadir was similar in both groups. In control s, increases in SMABF [42.4+/-6.1% (mean+/-S.E.M.); P < 0.001], cardiac out put (34.3+/-2.3%; P < 0.001) and pulse rate (from 63.9+/-2.7 to 82.5+/-3.1 beats/min; P < 0.001) occurred. Superior mesenteric artery resistance fell by 32.4 +/- 3.3% (P < 0.001). Under beta-blockade, decreases in SMABF (34.8 +/- 2.9%; P < 0.001) and pulse rate (from 59.5 +/- 0.2 to 51.8 +/- 2.2 bea ts/min; P < 0.001) occurred. Superior mesenteric artery resistance increase d (peak +30.8 +/- 12.3%; not significant). Subjects showed greater increase s in adrenaline (P < 0.006) and noradrenaline (P < 0.022) concentrations th an controls. Mesenteric hyperaemia associated with hypoglycaemia in man app ears to be mediated by a beta-adrenergic mechanism that is activated by inc reased circulating levels of adrenaline.