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Replacing Cis Octadecenoic Acid with Trans Isomers in Media Containing Rat Adipocytes Stimulates Lipolysis and Inhibits Glucose Utilization^1,2,3,

Animal, Dairy and Veterinary Sciences, Clemson University, Clemson, SC 29634

On the basis of earlier reports of reduced growth rate and fat accumulation in animals fed trans 18:1, a study was conducted to determine whether the effects of trans 18:1 on lipolysis and glucose utilization by adipocytes differed from effects of the cis isomer. Two experiments compared three fatty acid isomers (oleic, elaidic and vaccenic acids) at several concentrations and at several fatty acid to albumin ratios in cell media. Adipocytes were isolated from adipose tissue of rats by collagenase digestion and incubated for 2 h in media containing added fatty acids. Compared with oleic acid, both trans isomers reduced (P < 0.01) the amount of glucose converted to cell lipid in both experiments. Glucose oxidation to carbon dioxide also was lower for both trans fatty acids in Experiments 1 (P < 0.05) and 2 (P < 0.06). Lipolytic rates were increased (P < 0.01) in both experiments by replacing oleic acid with either of the trans isomers. Trans isomers of octadecenoic acid had catabolic effects on adipocyte metabolism that occurred regardless of the position of the double bond, the fatty acid concentration in media or the fatty acid to albumin ratio. These catabolic effects explain previous observations of reduced growth rate and fat accumulation when oleic acid in animal diets is replaced with a trans isomer.

KEY WORDS: • adipocytes • lipolysis • rats • trans fatty acids • glucose

¹ Presented in part at the joint meeting of the American Dairy Science Association and the American Society of Animal Science, July 12, 1994, Minneapolis, MN [Cromer, K. D., Jenkins, T. C. & Thies, E. J. (1994) Octadecenoate isomers induce changes in rat adipocyte metabolism in vitro. J. Dairy Sci. 77 (Suppl. 1): 71 (abs.)].

² Technical contribution no. 4004 of the South Carolina Agricultural Experiment Station, Clemson University, Clemson, SC.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ Current address: 159 Glassboro Road, Aiken, SC 29801.

⁵ To whom correspondence and reprint requests should be addressed.

Manuscript received 9 September 1994. Revision accepted 15 March 1995.