The objectives of this proposal are to obtain an understanding of the selective inhibition of fat intake by enterostatin, the aminoterminal pentapeptide of pancreatic procolipase. The hypothesis to be investigated is that enterostatin is secreted in response to the intake of dietary fat and acts as a feed-back regulator of fat intake. Excessive intake of dietary fat is thought to be a major factor in the development of obesity and the high incidence of cardiovascular disease but little is known of the physiological control of fat intake. We shall investigate the amino acid sequences and structural requirements for maximal biological activity of the peptide in the inhibition of fat intake, the regulation of synthesis and secretion of enterostatin, the site(s) of action of the peptide, its mechanism of action and its activity in a number of animal species in order to explore the physiological role of enterostatin. Enterostatin analogues will be synthesized and used to investigate the structural requirements necessary for the inhibition of fat intake after central and peripheral administration. The site of production of the peptide will be studied by Northern blot analysis using cDNA probes to parent molecules and an ELISA assay will be used to study serum and intestinal levels of enterostatin. With these techniques the regulation of synthesis and secretion of the peptide in response to dietary and endocrine manipulations that alter fat intake will be studied. As enterostatin is effective in reducing fat intake after both central and peripheral administration the possibility that enterostatin has a peripheral site of action will be investigated by studying the effects of enterostatin infused intravenously or into the gastrointestinal tract, and the possibility that this peripheral action is mediated through control of gastric emptying or at intestinal or hepatic sites via afferent vagus nerves will be studied. Central sites of action will be investigated by infusions of enterostatin into specific brain nuclei in rats stereotaxically implanted with guide cannulas. The interrelationship of the enterostatin inhibition of fat intake with the galanin stimulation of fat intake will be studied and the possibility that either or both of these systems are modulated through mu-opioid receptors will be explored in two ways. Firstly, the interactions of centrally injected enterostatin, galanin, and opioid agonists and antagonists in regulating fat intake will be studied; secondly, ligand binding assays will be used to identity specific receptors for enterostatin and investigate the possibility that enterostatin interacts directly with mu-opioid receptor systems. Finally we shall investigate the ability of enterostatin to suppress fat intake in other animal species (mice, dogs and baboons). As a result of these studies, we will gain important insights into the regulation of fat intake and the possible role that an endogenous peptide has in this process. This new information may be the impetus for a new therapeutic approach to treating obesity.