Effect of various doses of estrogen to BALB/cCrgl neonatal female mice on mammary growth and branching at 5 weeks of age.

High doses of 17beta-estradiol given newborn mice the first 5 days of life had no effect on mammary growth at 3 weeks of age whereas glands measured at 5 weeks of age displayed marked dose-dependent differences in area and branching. The number of duct branches increased significantly as the estrogen dose was raised from the 25 mug threshold to 35 or to 70 mug. Ratios between area and branching remained constant under all experimental conditions. Regional, dose-dependent, differences in gland-pair response were also observed at 5 weeks. Mammary gland pairs differed significantly in several growth parameters. The third gland pair was smaller in area and had fewer branches, but the opposite was true of the second and fourth gland pairs. Systemic injection of high doses of 17beta-estradiol into neonates reduced differences in growth parameters between gland pairs.