Evidence against a putative role for glucagon as a physiological splanchnic vasodilator in man

1. Previous studies have suggested that glucagon in supraphysiological doses may mediate postprandial and hypoglycaemia-induced splanchnic vasodilatation in man and experimental animals. There are no reported studies investigating the role of glucagon in doses producing circulating concentrations within the physiological range. 2. Two separate studies were performed. In study 1, superior mesenteric artery blood flow was measured by Doppler ultrasound in six normal subjects during either saline or glucagon infusion at 1, 3 and 6 ng min−1 kg−1, which resulted in circulating glucagon levels within the physiological range. Mean superior mesenteric artery blood flow fell during the 3 and 6 ng min−1kg−1 glucagon infusions (3 ng min−1kg−1: −31.8%, range −20 to −56% of baseline; 6 ng min−1 kg−1: −20.7%, range −8 to −53% of baseline; P < 0.05). 3. In study 2, superior mesenteric artery blood flow was measured during hypoglycaemia induced by an insulin infusion in 12 normal subjects. In six of these subjects the effect of suppression of glucagon release during hypoglycaemia was assessed by preteatment with the somatostatin analogue octreotide (0.8 μg/kg subcutaneously) given 30 min before the insulin infusion. 4. The nadir in blood glucose concentration at the hypoglycaemic reaction was similar in both groups and glucose recovery was complete by 60 min after the hypoglycaemic reaction. Plasma catecholamine concentrations rose in both groups after the hypoglycaemic reaction. 5. Superior mesenteric artery blood flow rose at the hypoglycaemic reaction in both groups despite suppression of glucagon release with octreotide. 6. These data suggest that at physiological concentrations glucagon does not mediate splanchnic vasodilatation in man.