Interactions between autonomic nerves and endocrine cells of the gastroenteropancreatic system.

Autonomic nerves and endocrine cells of both the gastrointestinal tract and the pancreatic islets participate in the control of several processes related to the digestion and metabolism of nutrients. While it was once thought that they acted separately to regulate these processes, it is now appreciated that numerous interactions exist between the functions of autonomic nerves and GEP endocrine cells. Recent studies show that autonomic signals play a role in the secretory activity of various GEP cells, thus providing a mechanism by which the central nervous system can integrate digestive and metabolic functions. It also has been shown that nerves and endocrine cells frequently share certain common peptides and/or amines. Therefore, in functional terms, it is often difficult to determine whether a specific peptide or amine should be considered a neurotransmitter or a hormone. Within the next few years, one can reasonably expect that new techniques and methods of investigation will clarify the roles of putative chemical messengers such as the peptides found within autonomic nerves and the amines found within endocrine cells. It also seems likely that future studies will demonstrate that the specific chemical messenger and the mechanism by which it reaches its target cells are far more important factors in the understanding of gastrointestinal and endocrine pancreatic function, than whether or not these signals are neural or endocrine in origin.