Blood glucose control by direct islet innervation.

Glucose tends to be elevated in situations of stress and an increase in plasma glucagon is an important cause. The rapidity of the glucagon rise in stress suggests a nervous mechanism. Electron microscopy has shown that the alpha and beta cells of the pancreas have, in fact, both an adrenergic and cholinergic innervation. Splanchnic-nerve stimulation has been shown in animals to cause a massive release of glucagon and marked inhibition of insulin. The glucagon response to hypoglycemia, on the other hand, appears to be significantly controlled by the parasympathetic system and, in man, is greatly attenuated after vagotomy. Thus there is a dual influence of the autonomic system on the islets of Langerhans, the sympathetic innervation elevating glucose in stress and the parasympathetic aiding glucose homeostasis.