In Vitro Metabolism of Glucose in the Isolated Fat Cells of Rats Inoculated with a Growth Hormone Secreting Tumor (MtT-W15)

Abstract

Hypersomatotropism was induced in Wistar/Furth fernale rats by inoculation of MtT-W15 tumor. Parametrial fat was removed from pair-fed animals at different periods after the inocu1ati~n of the tumor. Isolated fat cells were incubated with U-' C-glucose, and the conversion of 14 C into C02 and lipids was measured. The changes in the metabolism of glucose in adipose tissue developed in three stages. In the very early stage of hypersomatotropism (serum growth hormone 7-9 ng/ml) there was an increased glucose utilization both in the absence and presem:e of insulin. One to two weeks later, when serum growth hormone had risen to c1early hypersornatotropic levels (36-116 ng/ml) there was a decreased baseline glucose utilization, which could still be correeted by the addition of insulin. When the animals had had the growth hormone producing tumor for several weeks, depot fats were depleted, and the conversion of glucose to C02 and lipids was decreased both in the absence and presence of insulin.

Reduced glucose incorporation to triglycerides following chronic exposure of human fat cells to growth hormone

“…The present results show that the impaired in¬ corporation of glucose into total lipids (almost exclusively representing the glyceride-glycerol moiety in human fat cells; Smith, in press) after long-term exposure of human adipose tissue to GH was not accompanied by an altered CO2 formation. In rat adipose tissue studied in vitro other inve¬ stigators have found an impairment in CO2 form¬ ation as well as in lipid synthesis after long-term elevation of the plasma GH levels (Âkerblom et al 1971;Batchelor & Stern 1973). Since total glucose metabolism seems to be reduced by GH the me¬ chanism responsible is likely to be the membrane transport of glucose or one of the early steps in the glycolysis.…”

Insulin Sensitivity in Vitamin B₆-Deficient Rats

“…A kerbloom et al [1 ] have described a blunted response to insulin-induced 14C-glucose conversion to C 0 2 and lipid, in free fat cells of rats implanted weeks before with GH-producing tumors. The blunted response followed an early insulin-like phase.…”

“…The inhibitory second phase of GH action [1,10,13] is of greater interest because of its probably more important physiological significance. In the present study, the inhibitory effect of chronic GH administration was seen in adipose tissue and was significant only when insulin was present (tables III and IV).…”

“…This early insulin-like action of GH on hexose uptake in adipose tissue and muscle, and the pro duction of C 0 2 and fatty acid from glucose, has been noted by G o od m an [II,12], M ahler and Szabo [21], A kerbloom el al. [1], H ja lm a rso n [16,17], H jalm arson and A hren [18], and P a n d ia n et al [26], amongst others. Interestingly, acute GH treatment failed to more than minimally augment the insulin response in any of the groups except in adipose tissue glycogen.…”

“…In view of reported relationships of GH and insulin [1,7,21], the possibility appeared that altered GH metabolism might affect tissue sensitivity to insulin in vitamin BG deficiency. Studies of insulin sensitivity and its modification by GH in intact vitamin BG -deficient, pair-fed control and a d libitum fed control rats have been carried out.…”