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Effects of Adrenergic Agonists and Insulin on Porcine Adipose Tissue Lipid Metabolism In Vitro

U.S. Department of Agriculture^1,2,3,, Clay Center, NE 68933 and Texas A&M University⁴, College Station, TX 77843

Abstract

Because this laboratory has been able to demonstrate only a small and somewhat inconsistent stimulation of glucose metabolism by insulin in porcine adipose tissue in vitro, the tissue was preincubated with insulin to attempt to enhance the hormone effect. Preincubation with or without insulin did not increase insulin stimulation. Furthermore, insulin did not stimulate triacylglycerol biosynthesis. Adrenergic hormones stimulated lipolysis in porcine adipose tissue in vitro. Several analogs of norepinephrine incubated with porcine adipose tissue in vitro did not inhibit glucose incorporation into CO₂ or total lipids, in contrast to inhibition observed in adipose tissue from other species. Isoproterenol inhibited glycerol-3-phosphate incorporation into lipids; the maximal inhibition was 50% for the initial stages of the pathway. Palmitate incorporation into lipids also was inhibited 50% by isoproterenol but this may have been an artifact. Preincubation of adipose tissue, with no exogenous hormone, might decrease the concentration of endogenous adrenergic hormones and thus make the tissue more responsive to exogenous adrenergic hormones. Preincubation of porcine adipose tissue did not consistently lower the basal lipolytic rate but enhanced the stimulated lipolytic rate; the mechanism is not known. These experiments provide no evidence that preincubation is beneficial to measurement of lipolysis or glucose metabolism in porcine adipose tissue in vitro.

¹ Roman L. Hruska U.S. Meat Anim. Res. Center, ARS, USDA, Clay Center, NE. Location of D., C. Rule and H. J. Mersmann (author to whom reprint requests should be sent).

² We thank D. L. Ochsner, L. J. Robinson and C. J. Smith for execution of the glucose metabolism and lipolysis experiments; T. W. Acton and associates, especially J. A. Dague, for biopsy of pigs; Dr. M. D. MacNeil for statistical consultation; and M. M. Bierman for secretarial assistance.

³ Mention of trade names, proprietary products or specific equipment does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products that may also be suitable.

⁴ Dept. of Anim. Sci. Location of S. B. Smith. D. C. Rule was a research associate in the department; present address is Univ. of Colorado Health Sci. Center, Div. of Endocrinol., Denver, CO 80262.