[Effect of naloxone on beta-endorphin and insulin concentrations during glucose tolerance testing in patients with...

The concentrations of beta-endorphin, ACTH, insulin (IRI), glucagon (IRG), cortisol and growth hormone were determined by radioimmunoassay during oral glucose tolerance test (OGTT) performed in 13 obese patients with normal glucose tolerance and without arterial hypertension. The test was performed in random, before and after intravenous administration of 0.8 mg of naloxone. Six persons with normal body weight served as controls. Higher basal concentrations of beta-endorphin and significant increase in beta-endorphin levels during OGTT, without concomitant increase in ACTH concentrations, have been found in obese patients. No effect of naloxone on beta-endorphin liberation during OGTT was observed, though the drug caused lowering in maximal increment of beta-endorphin and paradoxically lowered the concentrations of ACTH and cortisol. The basal concentrations of beta-endorphin did not correlate with the concentrations of insulin, ACTH, cortisol and growth hormone. Elevated concentrations of insulin, lowered concentration of growth hormone and normal levels of glucose and glucagon were observed in basal conditions, and excessive responses of insulin, glucose and glucagon were observed in obese patients during OGTT. Naloxone lowered insulin response and inhibited the fall of growth hormone during OGTT but did not influence the concentrations of glucose and glucagon. No correlation was found during OGTT after naloxone between insulin and beta-endorphin, ACTH or cortisol, whereas negative correlation was observed between insulin and growth hormone. The obtained results suggest that the elevated concentrations of beta-endorphin in simple obesity may be of both hypophyseal and peripheral origin. Hyper-beta-endorphinemia observed in obesity is probably not directly responsible for hyperinsulinemia, it may, however, be responsible for lower sensitivity of tissues to the action of insulin.