An Evaluation of Peroxidase as a Marker for Estrogen Action in Normal Mammary Glands of Mice*

The present studies were initiated to study peroxidase and its possible regulation by estrogen in normal mammary glands. The activity of peroxidase was measured biochemically using guaiacol as the substrate for oxidation. Significant levels of peroxidase activity were associated with the particulate fraction of mammary glands from virgin mice, pregnant mice, and mice undergoing lactational involution. However, during lactation there was no detectable level of peroxidase activity in the mammary glands. Although ovariectomy led to a decrease in mammary peroxidase, detailed studies using various hormonal manipulations revealed that mammary peroxidase was perhaps not a product of estrogen action alone, but might be the result of a complex hormonal control related to growth. Alternatively, a critical evaluation of all of the data obtained with mammary glands and a comparison of these data obtained with the uterus also suggest that the presence of peroxidase in mammary glands may be due to infiltration of eosinophils and macrophages in these tissues resulting from mast cell degranulation.