STUDIES of GROWH HORMONE BINDING AND INSULIN LIKE METABOLIC EFFECT IN ISOLATED RAT ADIPOCYTES

Abstract

Adipocytes isolated by collagenase digestion from normal rat epididymal(EP), subcutaneous(SC), or retroperitoneal(RP) locations were selected for a study of human growth hormone(hGH) binding and metabolic activity. Scatchard analysis of 125-I-hGH binding was linear; binding affinities ranged from 2.1-3.5 × 109 M−1 and were not different, but the number of binding sites per cell were highest in EP(8,300), followed by SC(6,700), p<.05, and then RP fat(2,700), p<.01. The metabolic response of fat cells was evaluated by the incorporation of 14-C(U) glucose into adipocytes(without pre-incubation). With pituitary hGH, basal and maximally stimulated glucose incorporation was: EP=202±9 to 265±18 (31% increase, p<.05), SC=97±6 to 111±8 (17% increase), and RP=96±10 to 104±9 nMoles/106 cells(7% increase). Similar studies following biosynthetic hGH (supplied by Kabi Vitram) showed: EP=243±13 to 301±21(24% increase, p<.025), SC=120±17 to 139±31 (18% increase), and RP=110±10 to 104±12 nMoles/106 cells. Addition of hGH antibodies blocked the glucose incorporation in EP adipocytes using both pituitary and biosynthetic hGH, while insulin antibodies did not prevent this increase. We conclude that this insulin-like metabolic effect is caused by hGH, not an insulin-like impurity. EP fat cells demonstrated the highest number of binding sites and glucose incorporation, followed by SC and then RP fat cells. These results suggest different metabolic responses to hGH for adipose tissue from different locations.