Hormone-induced ductal DNA synthesis of human breast tissues maintained in the athymic nude mouse

Five biopsy specimens of morphologically normal human breast tissues, obtained from the margins of five benign human breast tumors, were processed into slices (4.0 x 4.0 x 0.1 mm) and transplanted s.c. dorsally (eight to ten slices/mouse) into forty-three 6- to 8-week-old female BALB/c athymic nude mice. Each individual human breast tissue specimen was transplanted into seven to ten mice. After 30 days, the mice were divided into four groups and treated for 30 days as follows: (a) controls receiving s.c. cholesterol pellets (38 mg); (b) estrogens that were administered in s.c. pellets containing 2 mg 17 beta-estradiol and 38 mg cholesterol and in drinking water containing 0.5 mg estrone per liter; (c) rat pituitary tumor (RPT), a cell suspension of MtT-W10 RPT that secretes large amounts of prolactin and growth hormone, injected dorsorostrally; and (d) RPT plus estrogens. Three to five human breast tissue grafts were removed from each mouse at the onset of treatment, and the remainder were removed at termination of treatment. DNA synthesis in the ductal epithelium was determined in pre- and posttreatment grafts by [3H]thymidine autoradiography after incubation of grafts for 4 hr in an isotope-enriched medium. The labeling index (LI), mean number of labeled epithelial cells per unit area of epithelial tissue, in pre- and posttreatment grafts was, respectively: (a) control, 7.6 +/- 1.4 and 7.1 +/- 1.4; (b) estrogens, 5.5 +/- 0.6 and 17.9 +/- 2.3; (c) RPT, 6.2 +/- 0.7 and 8.0 +/- 1.5; and (d) RPT plus estrogens, 6.3 +/- 0.8 and 26.6 +/- 2.5. A significant increase in LI was observed after treatment with estrogens (p less than 0.05) or RPT plus estrogen (p less than 0.001). Mean LI after treatment with RPT plus estrogens was significantly greater (p less than 0.02) than after estrogens alone. RPT alone did not significantly alter the LI. Thus, these results provide in vivo evidence that estrogens enhance DNA synthesis of the ductal epithelium of the normal human breast and that a growth factor (or factors) from RPT acts synergistically with estrogens to produce a more pronounced increase in DNA synthesis. RPT growth factors (perhaps prolactin and/or growth hormone) appear to require estrogens for DNA synthesis stimulation in normal human breast ductal epithelium.