Treatment of rats with growth hormone (GH; 1 mg/kg) s.c. twice daily over 2.5 days did not alter fasting plasma glucose or glucose tolerance, but increased fasting plasma insulin levels 64% and peak insulin response to a glucose load 35% over controls, indicating the development of insulin resistance. Studies on partially purified insulin receptors from soleus muscles showed that GH had no effect on insulin binding, but increased the abundance of insulin receptor β-subunits 27% as measured by immunoblotting. Despite this increase, GH abolished the increase in autophosphorylation of the insulin receptor β-subunit in response to physiological hyperinsulinemia, and diminished by 28% the response to supraphysiological hyperinsulinemia. Similarly, insulin- stimulated phosphorylation of IRS-1 was decreased 25% by GH but the abundance of IRS-1 was not affected. Studies on rats pretreated with streptozotocin suggested that the effects of GH are direct and not secondary to GH-induced hyperinsulinemia. Growth hormone decreased basal GLUT-1 abundance in the low-density microsome and plasma membrane fractions of epididymal adipocytes by 50 and 42%, respectively, but decreased basal GLUT-4 abundance only in the low-density microsome fraction by 24%. Despite these alterations, the abundance of both transporters in the plasma membrane fraction of adipocytes incubated with 0.1 U insulin/ml was not diminished by GH.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology