Dietary selenium regulation of glutathione peroxidase mRNA and other selenium-dependent parameters in male rats

Weanling male rats were fed a basal torula yeast diet (0.007 microg Se/g diet) supplemented with graded levels of Se (0 to 0.2 microg Se/g diet as Na₂SeO₃) (three rats/group) to evaluate classical glutathione peroxidase (GPX1, GSH:H₂O₂, oxidoreductase, EC 1.11.1.9) mRNA level as an indicator of intracellular Se status. Growth was followed throughout the dietary treatment and a number of Se-dependent parameters including liver GPX1 mRNA levels were determined after 33 days. Growth was not impaired at any level of dietary Se supplementation. In rats fed the Se-deficient basal diet, liver Se concentration was 5 ± 1%, liver GPXI mRNA levels were 10 ± 2%. plasma GPX activity was 2 ± 1%, erythrocyte GPX activity was 37 ± 1%, and liver GPX activity was 0 ± 2% of the levels in rats fed 0.1 microg Se/g diet; these parameters increased sigmoidally with increasing dietary Se, showing a breakpoint near 0.1 microg Se/g diet. Graphical analysis indicated that the increase in liver GPX1 mRNA level with increasing dietary Se, preceded the increase in liver GPX activity. Se supplementation had no effect on polyadenylated mRNA levels or on β-actin mRNA levels, demonstrating that Se regulation of GPX1 mRNA is specific. Se-deficient liver selenoprotein P mRNA levels were 69 ± 2% of the levels in rats fed 0.1 microg Se/g diet. We hypothesize that GPX1 mRNA is a primary target of the Se regulatory mechanism, making GPX1 mRNA level a potentially useful indicator of the status of an important intracellular regulatory pool of Se.