Dietary selenium requirements based on glutathione peroxidase-1 activity and mRNA levels and other Se-dependent parameters are not increased by pregnancy and lactation in rats.

The hierarchy of selenium (Se) requirements for growing rats ranges from <0.01 to 0.1 microg Se/g diet, depending on the choice of Se status parameter. To further evaluate the efficacy of molecular biology markers to determine Se requirements in later periods of the life cycle, which are less amenable to traditional approaches, we studied pregnant and lactating rats. Female weanling rats were fed a Se-deficient diet (<0.01 microg Se/g) or supplemented with graded levels of dietary Se (0-0.3 microg Se/g) for >10 wk, bred, and killed on d 1, 12, and 18 of pregnancy and d 7 and 18 of lactation; Se response curves were determined for 10 parameters including liver glutathione peroxidase (GPX). Growth, and mRNA levels for selenoprotein P, 5'-deiodinase, and GPX4 were not decreased by Se deficiency. GPX4 activity required 0.05 microg Se/g diet for maximum activity, similar to growing rats. Dietary Se requirements for plasma GPX3 activity decreased 33% in pregnancy, but returned during lactation to the requirement of growing rats. The Se requirement for GPX1 activity decreased 25% in pregnancy but not in lactation. GPX1 mRNA required 0.05 microg Se/g diet for maximum levels in both pregnancy and lactation, similar to growing rats. Clearly, Se requirements do not increase during pregnancy and lactation relative to Se requirements in growing rats. Unexpectedly, Se-adequate levels of GPX1 mRNA and activity declined to <40 and 50%, respectively, of nonpregnant Se-adequate levels during pregnancy and lactation, illustrating the need to fully understand biomarkers at all stages of the life cycle.