Direct tonic inhibition of insulin secretion by central nervous system.

An experimental animal model was developed to investigate the influence of the central nervous system (CNS) on insulin secretion via direct innervation to the pancreas. This model eliminates any indirect CNS effect on the pancreas by hormonal factors. It consists of a vascularly isolated, in situ perfused rat pancreas preparation with the cephalic portion of the animal functional, including innervation to the pancreas. Using this rat model, we have demonstrated that the nonstimulated rat brain exerts a tonic inhibition of glucose-stimulated insulin secretion in nonfasted rats. This inhibition can only occur directly via neurons from brain to pancreas, probably via the sympathetic nervous system. The brain does not alter the biphasic pattern of insulin secretion, but it suppresses the overall insulin secretory process throughout both phases of insulin secretion by a relatively constant degree ranging from 38 to 47%. The physiological purpose of this tonic suppression of insulin secretion is open to speculation, but it is well known that tonic sympathetic stimulation of the cardiovascular system represents an important physiological control mechanism. An analogous control may exist with respect to insulin secretion.