Influence of selenium status on activity of phospholipid hydroperoxide glutathione peroxidase in rat liver and testis in comparison with other selenoproteins

Selenium-deficient rats (-Se, fed a Torula yeast-based diet containing no added selenium for 6 weeks) were injected intraperitoneally with up to 50 mu g selenium per kg bodyweight (BW) and sacrificed 6 or 12 hr later. Control rats were fed a similar diet with 0.25 mg Se/kg diet added as sodium selenate. Phospholipid hydroperoxide glutathione peroxidase (phGSH-Px) and cellular glutathione peroxidase (cGSH-Px) activities were determined in liver and testis. Extracellular glutathione peroxidase (eGSH-Px) activity and selenoprotein P level were measured in plasma. Liver phGSH-Px activity in control rats was small in comparison with liver cGSH-Px activity. Much of the phGSH-Px activity measured in liver (especially under -Se conditions) was accounted for by non-specific NADPH oxidation, which was measurable in the absence of any added substrate in the reaction vial, or when a non-reactive substrate analogue was used. Gross activity of liver phGSH-Px fell only to 76% of control values in selenium deficiency and showed little response to selenium injection. Liver cGSH-Px and plasma eGSH-Px activities in -Se rats were reduced to <2% of control values under the same conditions, increasing after selenium injection only to 2 to 3% of control. Selenoprotein P level in plasma fell to 7% of control levels in -Se rats, returning to a maximum of 43% of control by 12 hr after injection of the highest selenium dose. In testis, phGSH-Px and cGSH-Px fell only to 65% and 45% of control values, respectively, and did not increase significantly in response to resupplementation of selenium under the conditions of this experiment. Based on activity levels, phGSH-Px appears to be of greater relevance in testis than liver. Activity of phGSH-Px in either tissue showed little change with selenium status. None of the peroxidases measured responded as strongly to short-term selenium repletion as did selenoprotein P.