AJP - Regulatory, Integrative and Comparative Physiology, Vol 259, Issue 3 627-R636, Copyright © 1990 by American Physiological Society

ARTICLES

Serotonin3 receptor antagonists block anorectic responses to amino acid imbalance

V. A. Hammer, D. W. Gietzen, J. L. Beverly and Q. R. Rogers
Department of Physiological Sciences, School of Veterinary Medicine, University of California, Davis 95616.

The role of serotonin3 (5-HT3) receptors in the initial food intake depression of rats ingesting amino acid imbalanced or high-protein diets was investigated. The 5-HT antagonists metergoline, pirenpirone, ICS 205-930, and MDL 72222, the dopamine antagonist pimozide, or the alpha-adrenergic antagonist phentolamine were injected 15-45 min before presentation of test diets. Food intake was measured at intervals for 3 days. The 5-HT3 antagonists, ICS 205-930 and MDL 72222, restored feeding of a mild isoleucine (Ile)-imbalanced diet to control levels, although MDL 72222 had a longer time course of action. ICS 205-930 also increased intake of a severe Ile-imbalanced diet and Thr-imbalanced diet but not a high-protein (44% casein) diet. Treatment with metergoline, which blocks 5-HT1, 5-HT2, and dopamine receptor sites but not 5-HT3 sites, increased intake of the basal diet at 3 and 6 h but did not significantly alter intake of the mild Ile-imbalanced diet. Although pimozide tended to increase intake of the mild imbalanced diet, neither dopamine nor alpha-adrenergic receptor antagonism significantly affected imbalanced diet intake. Thus 5-HT3 receptors may mediate the anorexigenic activity of 5-HT associated with feeding an amino acid-imbalanced diet.

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