Pancreatic Neuroendocrinology: Peripheral Neural Mechanisms in the Regulation of the Islets of Langerhans*

The islets of Langerhans are richly vascularized and both the islet cells and blood vessels are intimately associated with a variety of autonomic nerves. Direct electrical stimulation of the nerves in vivo or pharmacological stimulation of the islets with neurotransmitters in vitro results in changes in the rate of release of islet hormones. The purpose of this paper is to describe the anatomy of the islet in relation to its vascular supply and both motor and sensory autonomic nerves, which may play a role in altering the secretion rate of islet hormones. Evidence for catecholaminergic, cholinergic, and peptidergic nerves as well as possible peptide neurotransmitters in the pancreas is examined. Secondly, physiological and pharmacological studies are reviewed that reveal how efferent autonomic neural activity leads to altered islet secretion rates. Third, because the complex structure of the islet is supplied with a variety of autonomic nerves, the evidence for excitation of these nerves via reflex activation is examined.