Modulation by the hypothalamus of glucagon and insulin secretion in rabbits: studies with electrical and chemical stimulations.

The effects of electrical and chemical stimulations of the hypothalamus on the plasma levels of glucagon, insulin, and glucose were studied in undisturbed and free-moving rabbits. Electrical stimulation of the ventromedial hypothalamic nucleus (VMH) caused a marked increase in the circulating level of glucagon coincident with a rapid rise in the glucose level. The level of insulin did not increase during VMH stimulation, but increased after cessation of stimulation. Electrical stimulation of the lateral hypothalamic nucleus (LHN), on the other hand, did not alter the plasma level of either hormone. Microinjection of a minute amount of acetylcholine into the VMH led to a rapid increase in plasma glucagon, with a gradual rise in plasma glucose, but no significant change in the insulin level. The responses of glucagon and glucose to acetylcholine were almost completely blocked by previous treatment of the VMH with hexamethonium, but not with atropine. Microinjections of epinephrine and norepinephrine into the VMH also caused rises in the levels of both glucagon and insulin, although the effects of norepinephrine were much less than those of epinephrine. Injections of dopamine, serotonin, and gamma-aminobutyric acid had no effect. Chemical stimulation of the LHN only with epinephrine induced a preferential rise in the insulin level without any significant change in the levels of glucagon and glucose. It is concluded that the actions of acetylcholine in the VMH, probably though activation of nicotinic receptor, and of epinephrine in the LHN are important for hypothalamic modulation of the selective releases of glucagon and insulin, respectively. (Endocrinology 108: 605, 1981)