On the mechanism of action of dexfenfluramine: effect on alliesthesia and appetite motivation in lean and obese subjects.

This study investigated the intensity of two phenomena--perceived pleasantness of sweet tasting solutions, and subjective motivations related to eating--in lean and obese subjects. The study also examined the way in which dexfenfluramine influenced these phenomena as the basis of a mechanism underlying the action of dexfenfluramine on satiation. Such investigations had not previously been carried out on obese people. In lean subjects, glucose-induced negative gustative alliesthesia (NGA) was present but was not affected by drug administration. Dexfenfluramine did, however, markedly influence motivational ratings and subsequent food consumption in a test meal. In obese subjects, NGA was not present nor was it instated by drug treatment. Motivational ratings were strongly influenced by dexfenfluramine. Although hunger ratings were very low in obese subjects, they were further suppressed by the glucose load and by the drug. Hunger suppression was greater in obese than lean subjects. These results suggest that a decline in the pleasantness of a sweet taste is not a mechanism through which fenfluramine exerts an anorectic action. The data suggest that the suppression of subjective motivation to eat is implicated in the reduction of food intake by dexfenfluramine in lean subjects, and in the weight loss observed in obese people.