Effects of Growth Hormone on the Penetration of L-Arabinose Into Adipose Tissue11

Abstract

The accumulation of the metabolically inert pentose, L-arabinose-1-Cl4, in adipose tissue water was taken as an index of sugar penetration into fat cells. Epididymal adipose tissue was obtained from 100 g hypophysectomized rats, and growth hormone was administered in vivo or in vitro. The intracellular water volume was determined by subtracting the extracellular water volume (sucrose space) from the total water as determined gravimetrically. Bovine and ovine growth hormone (1 [mu]g/ml in vitro) significantly increased the penetration of L-arabinose into the epididymal fat cells of hypophysectomized rats and simultaneously increased the utilization of glucose in duplicate tissue segments. Pre-treatment of the donor rats with 50 [mu]g of growth hormone 30 min. before sacrifice increased the basal uptake of L-arabinose in vitro. This uptake of L-arabinose was not further increased by the addition of growth hormone in vitro. Three hr. after the intravenous administration of 100 [mu]g of growth hormone, the basal uptake of L-arabinose was not significantly changed, but the tissues failed to respond to growth hormone in vitro. Chronic treatment with growth hormone (50 [mu]g/rat/ day x 4) significantly decreased the basal uptake of L-arabinose and similarly rendered the fat insensitive to the action of growth hormone in vitro. The similarities between the effects of growth hormone on L-arabinose uptake and glucose utilization suggest that the effects of growth hormone on glucose metabolism in adipose tissue may result, at least in part, from changes in the rate of entry of glucose into adipose cells.