Decreases of plasma tryptophan concentrations following restricted feeding do not decrease serotonin and its metabolite in rat brain.

Rats trained on a restricted feeding (RF) schedule of 4 h/day were killed before (starved) and after (fed) the presentation of food to compare hepatic and brain tryptophan metabolism with feeding (FF) controls. The RF rats exhibited greater holo-tryptophan pyrrolase activity in the liver than FF controls. Holoenzyme activity of starved rats was greater than fed animals. Plasma levels of tryptophan higher in the FF rats were comparable in the starved and fed groups of RF rats. Plasma levels of glucose comparable in the FF and RF fed rats were smaller in the starved animals. Brain levels of tryptophan comparable in the RF fed rats and FF controls were smaller in RF starved rats. Brain concentrations of serotonin (5-hydroxytryptamine) and its metabolite 5-hydroxyindoleacetic acid comparable in the RF starved rats and FF controls were higher in the RF fed rats. Possible implication of the findings in the pathogenesis of food deprivation/starvation related disease, anorexia nervosa is discussed.