Postprandial metabolism and aversive response in rats fed a threonine-devoid diet

Lack of an indispensable amino acid in the diet induces a rapid reduction i n food intake. In this study, we assessed whether the anorectic signal afte r ingestion of a meal lacking threonine originated from either direct perce ption of the decrease in plasma threonine or from an indirect effect relate d to increased postprandial amino acid catabolism and energy expenditure. W e observed that 3 g of such a meal was sufficient to induce an aversive res ponse to the diet within 2 h. Postprandial changes to plasma ammonia and ur ea, urinary urea, and energy metabolism did not differ from those measured after a control meal. In contrast, plasma threonine levels fell within 1 h after the meal. It is concluded that an increase in postprandial energy exp enditure is not involved in the anorectic response to eating a threonine-de void diet. The drop in plasma threonine levels may be a potential signal, b ut the fact that the decrease in food intake occurred 1 h after the decreas e in plasma threonine questions a direct causal relationship.