THE ROLE OF ENDOGENOUS OLEIC-ACID PRODUCE D BY DELTA-9 DESATURASE IN THE SECRETION OF TRIGLYCERIDES IN HEPATOCYTES (EX-VIVO AND IN PRIMARY CULTURE)

Oleic acid increases VLDL secretion rate in vitro whereas dietary olei c acid exhibits a hypotriglyceridemic effect. In order to contribute t o clarify this discrepancy, we have studied the relationship between e ndogenous oleic acid produced by hepatic Delta 9-desaturase and the se cretion of VLDL-triglycerides. A first group of observations was obtai ned in two lines of fowl selected for high or low adiposity : hepatic Delta 9-desaturase and plasma VLDL-triglycerides concentration were hi gher in fat chickens than in lean ones. Second, in a primary culture o f chicken hepatocytes, we showed that inhibiting Delta 9-desaturase ac tivity with sterculic acid impairs VLDL-triglycerides, and demonstrate d that VLDL-triglycerides secretion is highly dependent on the Delta 9 -desaturase activity. We suggest to separately consider the effects of dietary oleic acid, and those of endogenous oleic acid which arises f rom Delta 9-desaturase in the endoplasmic reticulum, (i.e. at the very site of intracellular VLDL processing) and stimulates VLDL-triglyceri des secretion. In the chicken, oversecretion of VLDL-triglyceides and subsequent fattening could originate in a high hepatic Delta 9-desatur ation of saturated fatty acids.