Hypothalamic influence on insulin and glucagon release in the rat

Blood glucose, plasma insulin, and glucagon levels were measured in undisturbed and free-moving rats. The insulin and glucagon levels rise in the 1st min after the beginning of food ingestion, whereas the glucose level begins to increase only in the 3rd min if carbohydrate-rich food is eaten. This early rise in insulin and glucagon level is also observed under conditions in which carbohydrate-free food is eaten. A similar release of insulin and glucagon can be obtained by injection of 0.1 µg of norepinephrine into the ventromedial hypothalamus, but the same injection made into the lateral hypothalamus causes release of insulin only, whereas injections in other hypothalamic areas are nearly without effect. Similar injections of isoproterenol did not cause changes in insulin, glucagon, and glucose levels. It is suggested that the early insulin and glucagon responses are of reflex origin and that the ventromedial and lateral hypothalamic areas are relay stations in the reflex pathways. The lack of effect of atropine to block the insulin and glucagon responses to noradrenergic stimulation of the ventromedial hypothalamus indicates that the efferent pathway is not cholinergic