Evaluation of the control of glucagon secretion by the parasympathetic nervous system in man

To evaluate the influence of the parasympathetic nervous system on human glucagon secretion, we have measured the plasma immunoreactive glucagon (IRG) levels after the administration of edrophonium, bethanechol chloride, and 2-deoxyglucose, and have compared the IRG responses to hypoglycemia in normal, atropinized, and vagotomized man. Edrophonium administered i.v. and bethanechol chloride administered s.c. did not affect IRG levels. Two-deoxy-glucose resulted in symptomatic neuroglucopenia with resultant vagal discharge, as evidenced by increased gastric acid secretion; but no changes in IRG concentrations were observed. The IRG response to insulin-induced hypoglycemia in normal subjects was not influenced by the administration of atropine. In seven subjects with a truncal vagotomy and no increased gastric acid secretion during insulin-induced hypoglycemia, the IRG increases were indistinguishable from those of control subjects in terms of timing, peak level obtained, or total glucagon response. We conclude that the cholinergic system is unlikely to play an important role in modulating glucagon secretion in man.