Glycolic acid and tryptophan effects on feed intake and hypothalamic indoleamines in chicks

The effect of intraperitoneal injections of glycolic acid, glycine or tryptophan on feed intake and hypothalamic levels of 5-hydroxy-tryptamine (5-HT) and 5-hydroxy indole acetic acid (5-HIAA) was examined in chicks. Glycolic acid significantly depressed feed intake in a dose-dependent manner in comparison to saline or glycine, but only in birds injected with a level higher than 150 mg/kg body weight. The injection of glycolic acid or tryptophan but not glycine inhibited feed intake, and increased hypothalamic 5-HT and 5-HIAA 2 hr post-injection, as compared with saline injected controls. Blood plasma total lipids were elevated by all 3 compounds but plasma glucose was unaffected. The reduced feed intake obtained by injection of glycolic acid appears to result from an effect on the serotonergic system.