DIVERGENT REGULATION OF RAT ADIPOCYTE GLUT1 AND GLUT4 GLUCOSE TRANSPORTERS BY GH

The effect of GH, in vivo, on the glucose transport systems of rat adi pocytes has been investigated. Lowering of serum GH levels, by treatme nt of rats with an antiserum specific for rat GH (anti-rGH), significa ntly decreased serum levels of both IGF-I and insulin. Treatment with anti-rGH also increased glucose oxidation and the conversion of glucos e to lipid by isolated adipocytes. Adipocyte glucose oxldation and lip id synthesis were measured in the presence of a Limiting concentration of glucose and therefore reflect changes in glucose transport. Immuno blot analysis of adipocyte subcellular fractions revealed that anti-rG H induced an increase in the amount of the glucose transporters GLUT1 (1.6-fold) and GLUT4 (2.5-fold) present in plasma membranes and a decr ease (39%) in the amount of GLUT4 present in low-density microsomal fr actions. Lowering of serum GH also increased, by 36%, the amount of GL UT1 present in a total membrane fraction but had no such effect on GLU T4 levels. Replenishment of serum GH, by concurrent administration of ovine GH to rats, prevented all of these effects of anti-rGH. It was c oncluded that GH in vivo down-regulates the amount of both GLUT1 and G LUT4 present in rat adipocyte plasma membranes. This reflects a decrea se in the total cellular levels of GLUT1 and modification of the subce llular distribution of GLUT4 and results in restriction of adipocyte g lucose uptake.