Effects of conjugated linolenic acids on lipid metabolism and immune functions in rats.

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Conjugated linolenic acid (CLN) is a fatty acid that has 18 carbons with three conjugated double bonds composed of multiple positional and geometric (cis(c) and trans(t)) isomers. Conjugated linoleic acid (CLA), the representative conjugated fatty acid has been shown to reduce body fat in rodents. We previously demonstrated that body fat reducing effect of dietary CLN is at least comparable or even stronger than that of CLA in rats. The CLN used in the study was prepared by alkaline isomerization, and was a mixture of conjugated diene and conjugated triene. It is not clear whether the effects of synthetic CLN are common to all CLN isomers or responsible to some specific isomers. In nature, some seed oil contains a particular type of CLN as a main fatty acid component. Bitter gourd, pomegranate, catalpa and pot marigold contain alpha-eleostearic acid (9c,11t,13t-18:3), punicic acid (9c,11t,13c-18:3), catalpic acid (9t,11t,13c-18:3), and calendic acid (8t,10t,12c-18:3), respectively. In this project, we examined whether the CLN in these seed oils reduced the adipose tissue weights in male SD rats. Linseed oil containing alpha-linolenic acid (LN) was used as a control fat. After 4 wk on diets containing 0.7% of these fats, dietary punicic acid (pomegranate oil) lowered, whereas the other CLNs did not lower the weight of perirenal adipose tissue as compared with LN. Also, punicic acid increased the activity of hepatic beta-oxidation in mitochondria. This effect was also partly observed in rats pre-fed with the high-fat (20% lard) diet for 4 wk. It was, therefore, suggested that punicic acid in pomegranate oil was at least one of the factors for reducing adipose tissue weight in rats. In this study, we also measured serum concentration of immunoglobulin (Ig) A, IgG, IgM and IgE. However, the dietary fat-dependent effect was not significant.