Appetite regulation by serotoninergic mechanisms and effects of d-fenfluramine

In this literature review, evidence is presented for the theory that the neurotransmitter, serotonin (5-hydroxytryptamine, 5HT), in medial hypothalamic centres is an important regulator for appetite and for the selection of major food constituents. High local levels of 5HT cause a reduction of appetite and a preference for protein, low levels the opposite. The main antagonistic system is noradrenergic. The drug d-fenfluramine mimics the effects of 5HT by releasing 5HT from serotoninergic nerve endings and inhibiting its neuronal re-uptake. Further experimental data prove that a high-carbohydrate, low-protein diet promotes uptake of serum tryptophan in the brain and its conversion into 5HT. Hence, this serotoninergic system may function as a self-regulatory mechanism. In patients with decreased peripheral insulin sensitivity, the system may be disturbed, causing overconsumption of carbohydrates. This is sometimes compulsive ("carbohydrate craving"). It may be presumed that in the treatment of obesity, in addition to the use of serotoninergic drugs, successes with reducing diets may be enhanced by including periods of high-carbohydrate, low-protein intake. It would be worthwhile to explore whether similar alimentary self-regulatory mechanisms of neurotransmitter function exist in other regulatory systems.