Temporal Nature of Insulin Binding and Insulin-Stimulated Glucose Metabolism in Isolated Swine Adipocytes1

Abstract

Insulin binding and insulin-stimulated glucose metabolism were measured in swine adipocytes isolated from adipose tissue obtained by biopsy on 4 successive days. These characteristics were also measured in adipose tissue obtained on the 5th d immediately after exsanguination. Binding of 125I-insulin was measured at three different concentrations of unlabeled insulin (0, 1, 100 ng/ml) on each day. Specific binding (pg bound . 2 X 10(5) adipocytes-1 X 90 min-1) was not different (P greater than .05) for each insulin concentration among the 5 d. Specifically bound insulin increased (P less than .05) with increasing insulin concentration. The effects of insulin (0, 1, 100 ng/ml) on glucose oxidation and glucose conversion to lipid were also examined in biopsy (B) and postmortem (PM) adipocytes. For a respective insulin concentration, there was no difference in glucose oxidation or lipid synthesis over the 5-d (four B, one PM) sampling period. Lipid synthesis was stimulated by the presence of insulin (P less than .05; 1 and 100 ng/ml) when compared with basal incubations; however, glucose oxidation was unaffected by the presence of insulin. There was no difference in lipid synthetic rates between 1 and 100 ng/ml of insulin. The responsiveness of glucose oxidation and lipid synthesis to insulin in PM samples was identical to that for adipocytes from B samples. These results indicate: 1) that glucose metabolism and insulin binding to adipocytes isolated from swine adipose tissue obtained by biopsy did not differ from that in tissue samples obtained shortly after death and 2) that insulin-stimulated glucose metabolism and insulin binding did not fluctuate appreciably over a 5-d period when adipose tissue was obtained at the same time each day.