Superfusion of normal and neoplastic mouse mammary tissue with estrogens

Slices of normal mammary tissue from pregnant and lactating mice and slices of neoplastic (MXT) mouse mammary tissue were superfused with estradiol (E2) and estrone (E1) each labeled with a different isotope. Isotope concentrations in tissue and perfusate at the steady state were used to calculate fractions and rates of uptake, metabolism and release of estrogens by the tissue perfused. Both E2 and E1 entered equally well and were concentrated to the same extent by normal and neoplastic mammary tissue. However, much smaller tissue to medium ratios and larger diffusible fractions of estrogens were found in tumor slices as compared to mammary tissue from both pregnant and lactating mice, the uptake being the highest in pregnancy mammary glands. The interconversion between E1 and E2 was found to favor the formation of E2 in normal mammary tissue, the metabolic activity being the highest in lactating glands. In the MXT tumor slices the conversion of E1 into E2 was predominant as well but in contrast to the almost negligible metabolism of E2 in normal mammary tissue, a large fraction of E2 was converted into E1. The observed differences in estrogen uptake and metabolism between pregnant and lactating mammary glands were in concordance with the functional characteristics of the tissues. Furthermore, E1 was shown to play an important role in the mouse mammary gland as a metabolic precursor of E2. A different metabolic pattern was found in neoplastic mammary tissue.