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Stimulation of Lipogenesis by Insulin in Swine Adipose Tissue: Antagonism by Porcine Growth Hormone^1,2,

The Pennsylvania State University³, University Park 16802

Abstract

The effects of physiological (1, 10 ng/ml) and pharmacological (1,000 ng/ml) concentrations of insulin (INS) and porcine growth hormone (pGH) on lipid metabolism were determined in short-term (2 h) and long-term (26, 50 h) incubations of swine adipose tissue. The short-term effects of three different commercial sources of bovine serum albumin (BSA) on adipose tissue metabolism were also evaluated. Two of the three BSA preparations were found to be unsuitable for inclusion in the short-term incubation buffer because they caused a stimulation of lipid synthesis in adipose tissue and masked the stimulatory effects of insulin. Physiological concentrations of insulin stimulated glucose metabolism in 2-h incubations by 100% in adipose tissue from 80-kg swine. After a 26-h incubation period, INS maintained rates of glucose metabolism at levels comparable to maximally stimulated rates in fresh tissue. Insulin also enhanced glucose metabolism following 50-h incubations; however, rates were less than for 2- or 26-h incubations. Glucose metabolism was also stimulated in adipose tissue from 127-kg swine when incubated for 2 h with INS; however, INS responsiveness declined with increasing body weight. Lipogenesis and glucose oxidation were partially maintained by INS using tissue from the heavier swine. A pharmacological but not physiological concentration of pGH stimulated glucose metabolism in short-term incubations by 50% in adipose tissue from 80-kg swine, and by 10% in adipose tissue from 127-kg swine. Long-term culture of adipose tissue in the presence of pGH had no effect on glucose metabolism. Physiological levels of pGH directly antagonized the stimulation of glucose metabolism by INS in short- and long-term incubations. In summary, these results are the first to establish that swine adipose tissue is quite sensitive to insulin and that pGH directly antagonizes insulin action.

¹ Authorized for publication as paper no. 7248 in the Journal Series of the Pennsylvania Agr. Exp. Sta. Portions of this work were presented at the 7th Int. Congr. of Endocrinol. in Quebec City, Quebec (July 1 to 7, 1984) and at the 76th Amer. Soc. of Anim. Sci. Annu. Meet. in Columbia, MO (August 7 to 10, 1984).

² Mention of a trade name, proprietary product or specific equipment does not constitute a guarantee or warranty of the product and does not imply its approval to the exclusion of other products that may also be suitable.

³ Dept. of Dairy and Anim. Sci.