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

The Pennsylvania State University^,3, University Park 16802

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 10⁵ adipocytes^–1•90 min^–1) was not different (P>.05) for each insulin concentration among the 5 d. Specifically bound insulin increased (P<.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<.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.

¹ The authors would like to thank Vern Hazlett and David Hosterman for taking care of the swine and Jim Watkins, Donald Butts and Gerald Smeal for slaughtering the swine. This paper was authorized for publication as paper no. 6400 in the Journal series of The Pennsylvania State Univ.

² Author to whom all correspondence should be addressed: 301 Animal Industries Bldg., The Pennsylvania State Univ., University Park, PA 16802.

³ Dept. of Dairy and Anim. Sci.