Fish oil source differentially affects rat immune cell alpha-tocopherol concentration

We have previously reported that both the source of dietary fish oil and the chemical form of vitamin E supplied in the diet affect the vitamin E status of immune cells in rats. The purpose of this study was to investigate further the effect of fish oil source on immune cell vitamin E status using free alpha-tocopherol (alpha-T) at the AIN recommended level as the sole source of vitamin E. Sixty weanling female rats were fed semipurified, high fat (20 g/100 g) diets containing either tocopherol-stripped lard (LRD), menhaden fish oil (MFO), sardine fish oil (SRD) or cod liver oil (CLO) as the primary lipid source. Endogenous alpha-T concentration was measured and equalized to 150 mg/kg oil by addition of free RRR-alpha-T to each lipid source, allowing for a final concentration of alpha-T in the mixed diet of 30 mg/kg. An additional group of rats was fed LRD without supplemental vitamin E (LRD-) as a negative control. After feeding experimental diets for 5 or 10 wk, tissues were collected for alpha-T analysis by HPLC. After 5 wk, plasma and liver alpha-T (micromole alpha-T/g lipid) were significantly lower in SRD- and CLO-fed rats compared with LRD-fed rats. At 10 wk, only plasma alpha-T in CLO-fed rats remained significantly depressed. Plasma and liver alpha-T concentrations (micromoles alpha-T/g lipid) were not significantly lower in MFO-fed rats than LRD-fed rats at either time point. Compared with LRD, feeding MFO to rats for 5 or 10 wk resulted in significantly greater alpha-T content of immune cells. In similar fashion, SRD-fed rats, compared with LRD-fed rats, also had significantly greater alpha-T content in splenocytes at both time points and greater thymocyte alpha-T at 10 wk. In all instances, the alpha-T status of rats fed CLO was indistinguishable from that of rats fed the vitamin E-free diet (LRD-). These data further demonstrate the complexity of the relationship between vitamin E status and dietary (n-3) polyunsaturated fatty acids (PUFA)