REPLACING CIS OCTADECENOIC ACID WITH TRANS ISOMERS IN MEDIA CONTAINING RAT ADIPOCYTES STIMULATES LIPOLYSIS AND INHIBITS GLUCOSE-UTILIZATION

On the basis of earlier reports of reduced growth rate and fat accumul ation in animals fed trans 18:1, a study was conducted to determine wh ether the effects of trans 18:1 on lipolysis and glucose utilization b y 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 experime nts. 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 r ates were increased (P < 0.01) in both experiments by replacing oleic acid with either of the trans isomers. Trans isomers of octadecenoic a cid had catabolic effects on adipocyte metabolism that occurred regard less of the position of the double bond, the fatty acid concentration in media or the fatty acid to albumin ratio. These catabolic effects e xplain previous observations of reduced growth rate and fat accumulati on when oleic acid in animal diets is replaced with a trans isomer.