AJP - Regulatory, Integrative and Comparative Physiology, Vol 252, Issue 5 902-R914, Copyright © 1987 by American Physiological Society

ARTICLES

Acute effects of dietary protein on food intake, tissue amino acids, and brain serotonin

J. C. Peters and A. E. Harper

Male rats (100 g) previously adapted to a 20% casein diet were fed diets containing from 0 to 55% of casein and were killed after 20, 60, 150, 240, or 330 min. Food intake of rats fed a protein-free diet or a diet containing greater than 35% of casein was depressed within 20 min and remained depressed for up to 5.5 h. Depressed food intake of rats fed protein-free diets was accompanied by a rapid reduction in plasma and brain total concentrations of free indispensable amino acids (IAA). Food intake depression among groups fed diets containing in excess of 35% casein was associated with elevated plasma and brain total IAA concentrations, compared with those of animals fed diets containing 15-20% of casein. No consistent relationships were observed between food or protein intakes and whole-brain concentrations of 5-hydroxytryptamine, 5-hydroxyindole-3-acetic acid, or their sum. Our results suggest that in animals fed a single diet, food intake is depressed if the total concentration of free IAA in brain either falls below a certain critical minimum or exceeds some maximum tolerable level.

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