Effect of fenfluramine on insulin/growth hormone ratio in obese subjects

Obesity is characterized by increased levels of insulin and by subnormal growth hormone (GH) release. Insulin/GH ratio is significantly higher in obese than in lean individuals. Fenfluramine, an anorectic drug, may have some effects on hypothalamic-pituitary function and on insulin secretion, possibly through a serotonergic stimulation. The aim of this work was to study the effects of fenfluramine on the insulin/GH ratio after arginine in obese subjects. Ten volunteer obese females were studied; 10 volunteer women were the normal weight controls. All subjects were given placebo and fenfluramine (60 mg p.o.) in a randomized order and after 120 min underwent arginine infusion (25 g i.v. for 30 min). Blood samples were taken every 30 min until 270 min for GH and insulin radioimmunoassay. In the obese group the GH response to arginine was significantly lower than in controls. Fenfluramine administration restored the subnormal GH response to arginine in obese subjects. Arginine infusion provoked a greater insulin secretion in obese subjects than in lean individuals. Fenfluramine administration diminished the insulin response to arginine. Fenfluramine did not modify the insulin/GH ratio in controls while it significantly lowered the insulin/GH ratio in obese subjects. Because insulin promotes fat and carbohydrate storage while GH stimulates lipolysis, the combination of high insulin and low GH concentrations may worsen the obese condition. A lower insulin/GH ratio can be useful in the treatment of obesity.