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Effect of Adipose Tissue Site, Animal Weight, and Long-term Fasting on Lipogenesis in the Bovine^{1, 2, 3,}

Department of Animal Science, Iowa State University, Ames, Iowa 50010

The in vitro rate of acetate incorporation into long-chain fatty acids was used to measure the lipogenic capacity of adipose tissue taken from several sites of 278-, 385-, and 528-kg Holstein steers fed ad libitum and from 368-kg Holstein steers that had been fasted for 3 weeks. Effects of site, animal weight, and fasting on the rate of glucose oxidation and activities of glucose-6-phosphate (G-6-P) dehydrogenase and of NADP-isocitrate dehydrogenase also were determined. Subcutaneous adipose tissue (backfat) had a significantly higher lipogenic capacity than did internal (perirenal and omental) and intermuscular tissues which were similar. The lipogenic capacity, expressed on a tissue-weight or cytosol-protein basis, increased linearly with increasing animal weight. Rate of fatty acid synthesis in fasted steers was less than 1% of that in the controls (385-kg steers). The rate of glucose oxidation to CO₃ was highly correlated with the rate of fatty acid synthesis. Activity of G-6-P dehydrogenase varied with adipose tissue site, but did not differ significantly with animal weight and was not significantly correlated with either glucose oxidation or fatty acid synthesis. Activity of G-6-P dehydrogenase in fasted steers was about 50% of that in the controls. NADP-isocitrate dehydrogenase activity was reduced 32% by fasting. These data indicate that activities of these NADPH-generating enzymes do not seem rate-limiting for fatty acid synthesis in bovine adipose.

KEY WORDS: • lipogenesis • adipose tissue • bovine • fasting • NADPH-generating enzymes

¹ Journal Paper no. J-7877 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 1671, a contributing project to North Central Regional Project NC91.

² These data were taken from a thesis presented by the senior author to the Graduate College of Iowa State University as partial fulfillment of the requirements for the Master of Science degree.

³ These data were presented at the annual meeting of the Federation of American Societies for Experimental Biology, Atlantic City, 1972, Federation Proc. 31: 674 (abstr.).

Manuscript received 4 October 1972.