Insulin-stimulated glucose utilization in adipose tissue from rats bearing Walker 256 carcinoma

Male Sprague-Dawley rats (125--150 g) were implanted intramuscularly with Walker 256 carcinoma. After 10--14 days, tumor-bearing rats, alone with controls, were killed and the ability of insulin to promote the in vitro utilization of glucose by epididymal adipose tissue was assessed. The sensitivity of free adipocytes and minced adipose tissue from tumor-bearing rats to insulin, as assessed by measurement of the incorporation of glucose into total lipids as well as into the triglyceride fraction of neutral lipids, was significantly less (P less than 0.01) as compared to control animals. Similarly, insulin was considerably less effective at enhancing glycogenesis in vitro in adipose tissue from animals bearing the tumor for 10 days compared to adipose tissue from controls. Adipose tissue from tumor-bearing animals tended to convert less glucose to CO2 in the presence of insulin than did adipose tissue from controls. That this decreased in vitro sensitivity to insulin of adipose tissue from tumor-bearing animals could be the result of simple down-regulation by high levels of circulating insulin can be ruled out by the fact that the presence of the tumor resulted in lower circulating insulin than that in control animals. Serum glucose levels were also lower in tumor-bearing rats than in corresponding control animals.