Splenic responses to acute insulin-induced hypoglycaemia in humans

1. The effects of acute hypoglycaemia on the spleen were examined in normal humans using radioisotopic techniques, complemented by ultrasonic examination of the spleen. Hypoglycaemia had a modest effect on splenic area, measured by ultrasonography, which declined to 62 +/- 6% (mean +/- SEM) of the basal value after the onset of the acute hypoglycaemic reaction. 2. Hypoglycaemia had a pronounced effect on the splenic radioactivity, which decreased significantly to a mean of 10 +/- 7% of basal radioactivity at 15 min after the onset of hypoglycaemia. The splenic image completely disappeared at some time after hypoglycaemia in all subjects. 3. The reduction of splenic radioactivity was abolished during non-selective alpha-adrenergic blockade with phentolamine, but was unaffected by beta-adrenergic blockade with propranolol, or cholinergic blockade with atropine, which suggests that the response of vessels perfusing the spleen is mediated by alpha-adrenoceptors.