5-Hydroxytryptamine : a modulator of food composition but not quantity?
After a meal of protein, in contrast to a meal of carbohydrate (CHO) at 1915 hr, rats allowed to choose from high carbohydrate and high protein diets during 2000-2100 hr prefer CHO (1). Thus the hypothesis that this regulation of macronutrient selection involves brain 5-hydroxytryptamine (5-HT) metabolism was tested. Compared to three baseline days during which rats (250- 300g ) consumed 1 g CHO, rats fed tryptophan (TRP, 5-HT precursor; 15 mg in 1 g CHO) selected meals higher in protein concentration (35.4% vs 46.6%, F (1,12) = 20.05, p less than 0.001) from 10% and 60% casein diets during 2000-2100 hr. Associated with the higher protein selection was an elevated brain 5-HT turnover in rats killed 30 minutes after consuming CHO + TRP. Pretreating rats with p-chlorophenylalanine, an inhibitor of TRP hydroxylase, blocked this effect of TRP (36.3% vs 37.0%). Fenfluramine (1 and 2 mg/kg i.p. at 1945 hr), which transiently enhances neuronal 5-HT release, increased the rat's relative preference for protein from 28.8% to 37.5% (2 mg/kg, t = 3.21, p less than 0.025) during 2000-2100 hr. These rats, also exhibited a selective preference for CHO between 3-12 hrs post injection which paralleled the known subsequent depletion of 5-HT by fenfluramine. We conclude that the relative proportion of protein and carbohydrate selected in a meal is controlled, at least in part, by prior food effects on brain 5-HT metabolism.
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects; D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D010134:Fenclonine / Q000494:pharmacology; D005277:Fenfluramine / Q000494:pharmacology; D005518:Food Preferences; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000032:analysis / Q000502:physiology*; D014364:Tryptophan / Q000494:pharmacology
D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D005277:Fenfluramine; D012701:Serotonin; D014364:Tryptophan; D010134:Fenclonine