Specific binding of growth hormone by rat adipocytes.

Abstract

Human GH (hGH) binding by isolated epididymal fat cells was studied in nonhypophysectomized Wistar rats. Total binding of [125I]hGH was temperature and time dependent; nonspecific binding was maximal within 30 min of incubation at both 24 and 37 C. Equilibrium binding of [125I]hGH by small adipocytes (mean volume, 40–70 pl) from young lean rats (150– 220 g BW) at 24 C was reached at 90 min and remained stable for at least 3 h. At 2 h, nonspecific binding was 30% of the total radioactivity bound. Specific binding was demonstrable and directly related (r = 0.998; P < 0.001) to the number of cells present in the flasks from 0.2 to 2.4 × 106 fat cells/ml. The amounts of hGH specifically bound to small fat cells increased as the hGH concentration in the medium increased from 10 to 100 ng/ml, and remained at a constant level with further increments in medium hGH concentration. Several nonprimate GH preparations suppressed [125I]hGH binding to adipocytes, but did so to a lesser extent than biologically equivalen...