FENFLURAMINE AND OTHER SEROTONINERGIC DRUGS DEPRESS FOOD-INTAKE AND CARBOHYDRATE CONSUMPTION WHILE SPARING PROTEIN CONSUMPTION

Consumption of a carbohydrate meal accelerates brain serotonin synthesis (by increasing the ratio of plasma tryptophan to the sum of the concentrations of other neutral amino acids) whereas high-protein meals lack this effect. To determine whether the changes in brain serotonin following the consumption of particular foods influence subsequent food choices, the authors tested the effects of fenfluramine and related drugs, which presumably increase intrasynaptic serotonin levels, on the amounts of two diets presented simultaneously (5 % vs. 45 % protein, isocaloric, or 25 % vs. 75 % dextrin, isocaloric and isoproteiri) that rats choose to eat. Anorectic doses of fenfluramine caused rats to choose to eat greater proportions of the high-protein food or, when given isoprotein diets, to consume more of the low-carbohydrate food, i.e. the 25% dextrin diet. Fluoxetine, which blocks serotonin re-uptake, and MK 212, which stimulates serotonin receptors, had similar effects, but d-amphetamine did not. It is concluded that: (a) brain serotonin neurons do function as 'sensors', changing their release of neurotransmitter in response to what is eaten, and that these changes influence subsequent food choice; and (b) drugs like fenfluramine may be especially useful in treating obesity because they spare protein intake. © 1979 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.