A Comparative Study of the Effects of Insulin and Growth Hormone on Hexose Metabolism in Adipose Tissue

Abstract

Epididymal adipose tissue segments from hypophysectomized rats were incubated in vitro in the presence of growth hormone or insulin and various concentrations of glucose, mannose, fructose or galactose, uniformly labeled with C14. Both hormones significantly increased the uptake of all 4 sugars and their oxidation to C14O2. Both hormones also increased the incorpora?tion into fatty acids of C14 from glucose, mannose and fructose, but not galactose. Increasing the concentration of the sugars in the incubation medium brought about similar increases in hexose uptake and utilization. Insulin, but not growth hormone, increased the incorporation of C14 from glucose into glycogen, even when both hormones produced identical increases in glucose uptake, oxidation and conversion to fatty acids. These observations are consistent with the hypothesis that both growth hormone and insulin accelerate the entrance of hexoses into adipose tissue. The additional action of insulin, but not growth hormone, on glycogen synthesis strongly suggests that insulin does not mediate the effects of growth hormone.