Insulin action in growth hormone-deficient and age-matched control rats: effect of growth hormone treatment

The isolated effect of growth hormone on carbohydrate metabolism in rat ske letal muscle was studied in growth hormone-deficient dwarf rats (dw/dw) tre ated with either recombinant human growth hormone or saline for 10 days. In addition, age-matched heterozygous (DW/dw) (normal weight and plasma IGF-I ) control rats were treated with saline. Growth hormone increased weight ga in from 0.1 +/- 0.1 (S.E.M) to 3.6 +/- 0.1 g/day and plasma IGF-I concentra tion from 364 +/- 23 to 451 +/- 32 ng/ml. Glucose metabolism in skeletal mu scle perfused with basal, submaximal and maximal concentrations (0, 600 and 60 000 pmol/l respectively) of insulin was not changed by growth hormone. No change could be detected in the total number of glucose transporters (GL UT1 and GLUT4) in the skeletal muscles, except from a lower amount of GLUT4 in the soleus muscle in the heterozygous control group. However, at submax imal insulin concentrations, skeletal muscle glucose uptake and transport w ere significantly lower in the heterozygous control group compared with the growth hormone-deficient group. This could indicate either a direct long-t erm effect of growth hormone or more likely a secondary effect attributable to the difference in body weight (205.2 +/- 3.1 vs 361.6 +/- 5.9 g for dwa rf rats and heterozygous controls respectively), and thereby muscle fibre s ize, between the groups probably resulting in lower average interstitial in sulin and glucose concentrations at a given plasma concentration in the het erozygous rats. It is concluded that restoration of subnormal growth hormon e concentrations for 10 days has no effect on insulin-stimulated glucose me tabolism in skeletal muscle in vitro.