Peroxidase activity in the rat breast tissue as a marker of estrogen action.

Peroxidase activity and its inducibility by estrogen in the uterine and breast tissues of Holtzman rats varied with the age of animals. Basal proxidase level of the two tissues was low in immature and high in older animals. Estrogen induced significant peroxidase activity in the uteri of rats up to 56 days of age and thereafter the uterine response was poor. Though the breast tissue peroxidase response to estrogen was significant in 20-160 days old female rats, greater inducibility being noted between 40-90 days of age. Among the sex steroids, only estrogen could induce the enzyme in the breast tissue in a dose dependent way. Peroxidase was also induced appreciably in the male breast tissue to an extent observed in age-matched females. It is suggested that this enzyme could be regarded as a diagnostic end point of estrogen action in the rat breast tissue.