Effect of dietary protein on the peroxidation of eicosapentaenoic acid in stroke-prone spontaneously hypertensive rats.

In order to investigate the effect of dietary EPA on liver GSH peroxidase (GSH-Px) activity in rats, highly concentrated EPA (78% ethyl ester form) was administrated to SHRSP (Stroke-prone spontaneously hypertensive rat) that were fed a casein, SPI (soybean protein isolate) or SPI diet with methionine for 4 weeks. The content of liver GSH in rats fed SPI was lower than that of rats fed the casein diet. Although no significant difference of liver GSH-Px was observed in rats after EPA supplement, a decrease of liver GSH-Px activity was found in rats fed the SPI diet when compared with rats fed the casein diet. The changes of liver GSH content and GSH-Px activity in rats fed SPI were found to be associated with methionine supplement. Addition of methionine to the SPI diet resulted in an increase of liver GSH content and GSH-Px activity. In addition, liver lipid peroxide concentration was increased in rats fed the SPI diet after EPA treatment. In contrast, EPA administered rats fed the SPI diet containing methionine showed a lower liver lipid peroxide concentration. These results suggest that methionine may play an important role in regulation of the utilization of EPA in SHRSP when fed a SPI diet.