Neural and Hormonal Regulation of Gastrointestinal Function: An Overview

During the past decade physiologists have been so preoccupied with the newly isolated peptide hormones of the gut that nerves have been neglected. This imbalance is now being redressed because we are learning that nerves are more important than we have supposed. The interactions between nerves and hormones are pervasive. For an understanding of gastrointesti­ nal regulation it is usually necessary to study both. Since all gastrointestinal hormones had been found to be peptides, it was assumed that the converse was also true-i.e. that all biologically active gastrointestinal peptides are hormones. It is now apparent that this is not so. Some gastrointestinal peptides are in nerves and some are in endocrine­ like cells which, however, do not discharge their product into the blood and therefore are presumed to perform a paracrine function. The recent discov­ ery that many peptides are found in both neurons of the brain and endocrine cells of the gut (20) has revolutionized our ideas about how the activities of the digestive tract are regulated.