Effect of alpha adrenoreceptor stimulants infused intrapancreatically on glucagon and insulin secretion

To see the effect of alpha adrenergic receptor stimulation upon in vivo basal secretion of glucagon and insulin, phenylephrine and methoxamine were infused at a dose of 236 pmol/kg/min and 2.36 nmol/kg/min, respectively, for 10 min into the cranial pancreaticoduodenal artery in anesthetized dogs. During the infusion of either drug pancreatic venous blood flow was markedly diminished, resulting in a significant decrease of basal output of both glucagon and insulin. Intrapancreatic administration of the stimulants exerted neglible effects on the plasma levels of both hormones in the systemic circulation. Pretreatment with phentolamine abolished the alpha stimulant-induced inhibition of bihormonal output. Under alpha blockade which per se results effectively in a stimulation of insulin release, basal output of glucagon was not significantly augmented. These results suggest that the alpha receptors on the A cell of the islets may be involved in the similar inhibitor mechanism, but less potently than those on the B cell under basal physiological adrenergic control in the canine.