REDUCED GROWTH-HORMONE RESPONSE TO L-DOPA AND PYRIDOSTIGMINE IN OBESITY

The purpose of this study was to evaluate growth hormone (GH) secretio n and clarify the factors influencing GH secretion in obesity. Nine ob ese subjects and eight controls were recruited. We compared the GH res ponse to L-dopa with or without pyridostigmine pretreatment in obese a nd control subjects. Plasma glucose, insulin, insulin-like growth fact or I (IGF-I) and free fatty acid (FFA) were also measured. Growth horm one responses and GH area under the response curve (AUC) to L-dopa wer e significantly lower in obese subjects than those in controls. Pyrido stigmine significantly enhanced the GH response to L-dopa in both obes e and control subjects. However, enhanced GH responses in obese subjec ts were attenuated biologically and lower than those in controls with L-dopa only. Plasma levels of insulin and FFA were significantly highe r in obese subjects than those in controls. Body mass index had a posi tive correlation with the levels of insulin and FFA. However, GH AUC h ad an inverse correlation with insulin and FFA in obese subjects and c ontrols. Stepwise multiple regression analysis showed a highly signifi cant effect of FFA on GH AUC, but no independent influence of other fa ctors on GH AUC. The reduced GH secretion found in this study suggests an increase in somatostatinergic tone and a diminished release of GHR H from the hypothalamus in obesity. However, other factors including h yperinsulinemia and increased plasma FFA may play an important additio nal role in the secretory dysfunction of GH in obesity.