Under-responsiveness of growth hormone secretion after L-dopa and deep sleep stimulation in obese subjects

Plasma levels of glucose, free fatty acids and free 11-hydroxycorticosteroids, and serum levels of immunoreactive human growth hormone (HGH) and immunoreactive insulin were determined before and after L-dopa stimulation in 18 obese and six normal-weight subjects. A blunted response of HGH was found in the obese subjects who received 0.5 g L-dopa, but when the dose was doubled, a normal response was obtained in 7 of 13 of the obese subjects. No significant fluctuations in free 11-hydroxycorticosteroid, glucose or insulin levels were found in the obese and normal-weight groups and no increase in HGH was seen in the obese group after the subjects had been asleep for 90 min. In the obese subjects, the blunted response of HGH to stimulation with 0.5 g L-dopa and the lack of HGH increase during sleep are attributed to hypothalamic under-responsiveness, which is considered a basic disturbance in obesity.