Ayman I. Sayegh, Ph.D. - US grants

DESCRIPTION (provided by applicant): The goal of this application is to determine the physiological role of gastrin releasing peptide (GRP), released by the enteric neurons of the gastrointestinal tract, in the regulation of meal size in rats. Despite accumulating evidence that support such role, two fundamental questions remain unanswered: (1) Is GRP a physiological signal that regulates meal size? (2) If indeed GRP is a physiological signal that regulates meal size, then how does it do that? This application attacks these questions by providing a decisive test of the hypothesis at risk: Gastrin releasing peptide, released in response to nutrients, regulates meal size by first activating the enteric nerves of the gut, which in turn activates the extrinsic innervation of the gastrointestinal tract and then the feeding control areas of the dorsal vagal complex of the hindbrain. Four Specific Aims will test this hypothesis systematically. (1) Determine the physiological role of endogenous GRP in regulating meal size. (2) Determine the gastrointestinal site of action of endogenous GRP responsible for regulating meal size. (3) Determine the role of enteric neuronal GRP in regulating meal size. (4) Determine the afferent pathway that GRP utilizes to regulate meal size. First, to determine the physiological role of GRP in regulating a normal meal size, we will use the spontaneously feeding undisturbed rat preparation to characterize individual meals by recording second-by-second intakes of liquid diets using lickometers and a reliable and valid behavioral observation scale. Following that, we will employ potent, and highly selective, receptor antagonists and antibodies to reverse the effect. Second, to determine the gastrointestinal site of action of endogenous GRP on meal size we will deliver GRP to organ-selective abdominal sites by close-arterial infusions and measure meal size. Our preliminary results have shown that one site of action of GRP lies in the vascular bed of the left gastric artery. Third, to determine the role of the enteric neurons in GRP-regulation of meal size we will employ chemical and surgical ablations of these neurons combined with detection of Fos-like immunoreactivity (Fos-LI;a marker for neuronal activation) while measuring the effect on meal size. Forth, to determine the afferent pathway that GRP utilizes to regulate meal size we will perform selective ablations of extrinsic abdominal nerves (vagotomy, sympathectomy and both) and measure meal size and Fos-LI in response to exogenous and endogenous GRP. In this application we propose that: (1) GRP makes an important physiological contribution to the regulation of meal size. (2) The myenteric neurons of the gastrointestinal tract comprise the site of action of GRP to regulate meal size. (3) The enteric nervous system of the gastrointestinal tract has a role in the regulation of meal size by GRP. (4) The vagus and / or the sympathetic nerves have a role in transmitting the GRP-satiation signal from the enteric neurons to the hindbrain. PUBLIC HEALTH RELEVANCE: Obesity is a common clinical problem especially in the African American community. This disease results from poor control of food intake and poor understanding of the processes that regulate it. The proposed research will investigate the role of the hormone gastrin releasing peptide in the regulation of food intake.

PROJECT SUMMARY (Project 1) Treatment of obesity requires an understanding of the mechanisms that regulate the short-term control of food intake, i.e., factors that reduce individual meal size (MS); prolong the time between two consecutive meals, known as the inter-meal interval (IMI); and result in reduction of body weight. The proposed effort will involve evaluation of the anti-obesity effects of the short-term satiety peptide, gastrin-releasing peptide (GRP) by testing the hypothesis that, if, in diet-induced obese rats, GRP is injected in low amounts and at highly specific gastrointestinal sites, it effectively and safely reduces MS and extends the IMI (i.e., increases satiety), resulting in reduction in body weight. There are three Specific Aims: Specific Aim I: Determine the specific gastrointestinal site(s) of action controlling MS, IMI length, and body weight (BW) by endogenous GRP released by a normal meal. Specific Aim II: Determine the specific gastrointestinal site(s) of action controlling MS, IMI length, and BW by exogenous GRP-10 (a COOH-terminal decapeptide of GRP) and GRP-29 (a large molecular form of GRP). Specific Aim III: Determine the specific gastrointestinal site(s) of action controlling MS, IMI length, and BW by endogenous GRP released by peptone. In addition, the safety of infusions of the peptides and antagonists will be evaluated by examining the morphology and weights of the specific gut sites of action following single and chronic infusions of GRP. We will test these three aims by innovative approaches, including use of (a) microvascular catheterization of the major arteries and their branches in the gut, (b) a sensitive enzyme immunoassay that determines the levels of GRP in response to meals; (c) immunohistochemical detection of Fos-like immunoreactivity, a marker for neuronal activation in the enteric neurons and in the dorsal vagal complex; (d) diet-induced obese rats; and (e) the automated BioDAQ feeding apparatus. This work will establish, in diet-induced obese rats, the specific site(s) of action regulating meal size, IMI, and BW by endogenous and exogenous GRP and will determine if GRP can be tested in humans as an anti-obesity medication.