INFLUENCE OF GROWTH HORMONE ON THE SENSITIVITY OF RAT DIAPHRAGM TO INSULIN

Abstract

ABSTRACT The in vitro effects of insulin (0.1—1.0 mU/ml) on the rate of intracellular accumulation of 14C-labelled α-aminoisobutyric acid (AIB-14C) and D-xylose-14C were much more pronounced in the intact diaphragm from hypophysectomized rats than in that of normal rats. Similar differences in sensitivity were also found for GH (25 μg/ml). Injections of GH intramuscularly for 4 days or intravenously together with the glucocorticoid dexamethasone 3 hours before start of incubation did not reduce the in vitro effect of insulin (0.1 and 0.5 mU/ml) on the uptake of D-xylose-14C in the diaphragm from hypophysectomized rats. The injection of both GH and dexamethasone significantly decreased the uptake of D-xylose-14C both in the presence and absence of insulin. Preincubation of the diaphragms from hypophysectomized rats with GH (5 μg/ml), which has been found to completely abolish the subsequent effect of GH (Hjalmarson 1968), did not reduce the effect of insulin (0.1 mU/ml) on the accumulation of AIB-14C and D-xylose-14C. Neither did dexamethasone (0.1 μg/ml) change the sensitivity to insulin in a similar experiment. However, preincubation with both GH and dexamethasone for 3 hours significantly reduced the accumulation rate of AIB-14C and D-xylose-14C in the diaphragms both in the presence and absence of insulin (0.1 and 1.0 mU/ml). This pretreatment also reduced the effect of insulin on the uptake of AIB-14C in diaphragms from both normal and hypophysectomized rats. No such insulin antagonistic effect of GH and dexamethasone in vitro was, however, obtained on the accumulation of D-xylose-14C.