Normal and Neoplastic Development of the Mouse Mammary Selenium Concentration and Glutathione Peroxidase Activity in

This study was divided into three experiments, (a) The levels of selenium and glutathione peroxidase (GSH-PX) activity were determined for various developmental states of the mammary gland: normal (virgin, pregnant, and lactating); preneoplastic hyperplastic outgrowth lines; and neoplastic mammary tissues. Tissues from the pregnant and lactating mice had higher sele nium concentrations and GSH-PX activities than did tissues from virgin mice, but the levels were similar to levels found in preneo plastic and neoplastic mammary tissues of lines C4 and D2. This suggests that the appropriate comparisons for studies determin ing the effect of selenium on preneoplastic mammary tissues are glands from pregnant and lactating mice. In addition, these results suggest that the refractory state of mammary tumors to selenium-mediated growth inhibition is not due to the absence of GSH-PX or the inability to incorporate selenium, (b) For the second experiment, the effect of feeding various levels of sele nium on selenium and GSH-PX levels was determined in mam mary and hepatic tissues of virgin mice. GSH-PX activity in creased when dietary selenium increased from less than 0.02 to 0.1 ppm selenium but was not further increased when dietary selenium was above 0.1 ppm. (c) Finally, the mammary GSH-PX activity was evaluated at different concentrations of the sub strates in order to document the biochemical characteristics of the mammary gland GSH-PX.