Vagotomy or atropine blocks hypoglycemic effect of insulin injected into ventromedial hypothalamic nucleus.

Stereotaxic microinjections of insulin (100 microU) into the ventromedial hypothalamic nucleus (VMN) resulted in rapid decrease, whereas injection of control saline into the same region caused a slight increase of hepatic venous plasma glucose concentration in rats. The hypoglycemic effect of insulin injected into the VMN was eliminated by pretreatment of the animals with atropine but not with propranolol or with phentolamine. Subdiaphragmatic vagotomy also prevented the decrease of hepatic venous plasma glucose concentration seen after microinjection of insulin into the VMN. These results support the hypothesis that the VMN is an insulin-sensitive glucoregulator center or that it is part of one and that the glucoregulatory impulse that originates in the VMN reaches the effector organ, the liver, through the cholinergic fibers of the vagus nerves.