INHIBITING DELTA-9-DESATURASE ACTIVITY IMPAIRS TRIACYLGLYCEROL SECRETION IN CULTURED CHICKEN HEPATOCYTES

The relationship between endogenous oleic acid produced by hepatic Del ta 9-desaturase and the secretion of VLDL-triglycerides was investigat ed in a primary culture of chicken hepatocytes. When the fatty acid co mpositions of the secreted and intracellular triglycerides (TG) (or tr iacylglycerols) were compared, an imbalance between monoenes and satur ated fatty acids was observed, with the secreted TG being significantl y more unsaturated than the intracellular TG. The addition of a mixtur e of cyclopropenic fatty acids (specific inhibitors of fatty acid desa turation) to the culture medium of cells 24 h before measurement of th eir Delta 9-desaturase activity and TG secretion rate caused a signifi cant impairment of both desaturase activity and TG secretion, without affecting total TG synthesis. However, the addition of oleic acid to t he culture medium of cells treated with cyclopropenic fatty acids rest ored the TG secretion rate. Palmitic acid did not restore the TG secre tion rate and linoleic acid partly restored the TG secretion rate. Fin ally, even in the presence of oleic acid in the culture medium of secr eting cells, those which had been treated with cyclopropenic fatty aci ds had a significantly lower TG secretion rate than nontreated cells. Taken together, these results show that TG secretion is highly depende nt on the Delta 9-desaturase activity and suggest that oversecretion o f VLDL-TG in chickens and subsequent fattening could originate in a hi gh hepatic Delta 9-desaturation of saturated fatty acids.