Cholecystokinin (CCK) peptides are known to be essential regulators of gastrointestinal function and are believed to play an important role in neuronal activity. Recent studies have implicated CCK receptors in the mediation of satiety suggesting that a disfunction of this system could be a major factor in the development of obesity. This proposal has two objectives relative to the study of CCK systems. These are the characterization of new CCK peptide analogues and the characterization of gastrin receptors and CCK receptor subtypes. CCK peptide analogues will be characterized for binding affinity and biological activity at three receptor types. These include the two major CCK receptor types (CCK-A and CCK-B) and the gastrin receptor. CCK-A receptors are defined here as the guinea pig pancreatic CCK receptors labeled by low concentrations of Bolton-Hunter iodinated CCK-8 while CCK-B receptors are defined as those labeled by the selective CCK-B receptor radioligand [N- methyl Nle28,31]CCK-8 in guinea pig cortex. Gastrin receptors are defined as those labeled by iodinated gastrin-1 in guinea pig gastric glands. The biological activity (agonist or antagonist) of the analogues will be measured using guinea pig ileum and gall bladder contraction assays (CCK- A), Ca2+ mobilization using NCl-H345 small cell lung cancer cells (CCK-B), and as the stimulation of gastric acid secretion (gastrin). The radioligand binding and biological assays will provide essential information to the members of Project A for the design of new analogues. The second part of the project will further characterize subtypes of the CCK-A and CCK-B receptors and will define pharmacological differences between CCK-B and gastrin receptors. These studies will test the hypothesis that: (1) There are G-protein coupled and uncoupled CCK-B receptor subtypes in guinea pig brain, (2) That pancreatic CCK-A binding sites include a population of CCK-A receptor subtypes with low affinity for CCK-8 and (3) That the gastrin receptor of gastric tissue is distinct from the CCK-B receptor of cerebral cortex.
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