Rapid and transitory stimulation of 3-O-methylglucose transport by growth hormone

The regulation of hexose transport by growth hormone (GH) was investigated using isolated rat adipocytes. GH caused a rapid (less than 3 min) rise in rates of 3-O-methylglucose transport that reached a maximum of two to six times the basal rates in 10-30 min. The stimulation of transport was transitory, and rates of transport started to decline 15-30 min after GH was added. Transport stimulation required a period of preincubation; no stimulation was observed in freshly isolated cells. GH stimulated hexose transport between 100 and 5,000 ng/ml, with a 50% effective dose between 200 and 300 ng/ml. Depletion of cellular ATP by 2,4-dinitrophenol blocked the ability of GH to stimulate transport but not the decline of transport rates following stimulation by GH. In contrast, an inhibitor of RNA synthesis, actinomycin D, had no effect on either the initial stimulation by GH or the initial subsequent decline of transport when added simultaneously or 15 min prior to GH. Actinomycin D did, however, cause a second rise in hexose transport at approximately 120 min that was blocked by 2,4-dinitrophenol. These results suggest that changes in glucose transport contribute to the effects of GH on carbohydrate and lipid metabolism in adipose tissue. These changes are rapid, of substantial magnitude, and of a complex nature, suggesting that regulation of glucose transport by GH most likely involves multiple mechanisms.