Novel pathway of metabolism of alpha-linolenic acid in the guinea pig

Docosahexaenoic acid (DHA) plays an important role in the nervous system. T he capacity of the infant to use the essential fatty acid alpha-linolenic a cid (ALA) as a substrate for neural DHA has been the subject of much debate recently. In this study, we explored the metabolic fate of an oral dose of C-14-labeled ALA in guinea pigs fed a defined diet for 3 wk from weaning. Of the C-14-labeled ALA administered, more than 46% was associated with the skin and fur lipids, mostly in the FFA fraction, and less than 0.1% was in brain lipids. About 39% of the label was not recovered in the body lipids and was assumed to be expired as CO2 or unabsorbed. The fur and skin were a lmost equally labeled; however, because of the very low mass of ALA in the fur, the specific activity of the fur was very high. These data identify a new route of metabolism of ALA in this species, presumably through the seba ceous glands onto fur. If this pathway exists in other species, including h umans, it may account for the poor efficiency of conversion of ALA to DHA, because dietary ALA would not be available for anabolic pathways such as DH A synthesis. The relevance of these data to infants is that ALA may play an important hitherto unidentified role in the skin related to barrier functi on or epidermal integrity. This calls for more research into the importance of ALA as an essential fatty acid in its own right in human infants.