This proposal concerns the post-secretory metabolism of neuropeptides in the musculature of the human stomach. The thesis of the proposal is that peptidase enzymes on the surface of cells degrade and inactivate neuropeptides int he interstitial fluid and thereby make an important contribution to physiological control. When a nerve fiber is stimulated, neuropeptides are released into the interstitial fluid and diffuse through the intercellular spaces towards receptors on the surface of nearby cells. The peptides bind to the receptor and initiate a cascade of intracellular events that trigger a change in function of the target cell. The two basic criteria that must be met before a molecule can be considered a neurotransmitter have been satisfied for many neuropeptides: release from a nerve and receptor-mediated action on target cells. However, a crucial part of the neurotransmitter theory has been neglected: what is the mechanism of inactivation of the neuropeptides? The general hypothesis is that cell-surface peptidases degrade and activate receptors. Therefore, peptidases limit the sphere of influence of the neuropeptides and contribute to physiological control by modulating their biological actions. The proposal focuses on the metabolism of three neuropeptides that make a major contribution to the control of gastric motility: substance P, enkephalins and vasoactive intestinal peptide. The six specific aims are designed to answer the general question: what is the physiological role of neuropeptide degrading enzymes in the muscular layers of the human stomach? Specific aim I examines the degradation of neuropeptides by membrane- associated peptidases in gastric muscle. Specific aim iI proposes the isolation of the major enzymes by column chromatography and examination of their enzymatic and chemical properties. Specific aim III concerns the immunocytochemical localization of peptidases with peptide-containing nerves and peptide receptors. Specific aim IV proposes to use enzyme inhibitors to discover the physiological roles of peptidases in the regulation of gastric motility. Specific aim V examines the mechanisms that control the expression of neuropeptides and their peptidases in the stomach wall. Specific aim VI proposes the design of long-acting peptides that resist peptidase degradation in tissues and blood and are clinically useful. The results derived from this proposal will provide an insight into the contribution of neuropeptides and their peptidases to the regulation of digestion in both health and disease states and will facilitate the design of long-acting peptides and peptidase inhibitors of therapeutic value.