The effects of progestins and glucocorticoids on cellular proliferation were examined in the uterus of 5-day-old mice by monitoring either the labeling index (LI) after exposure to [methyl-3H]thymidine ([3H]TdR) in vivo or the mitotic index (MI) after colchicine-induced arrest of cells in metaphase. In untreated 5-day-old mice, epithelial LI was 31%, and stromal LI was 15%. Eighteen hours after a single ip injection of 40 mg/kg progesterone, epithelial LI was reduced to 2.3% and remained low for 48 h. Stromal LI increased transiently, reaching a zenith (40%) 18 h after administration of progesterone and returning to control levels by 24 h. When mitotic activity was assessed 24 h after progesterone treatment, epithelial MI was decreased (control, 3.1%; progesterone, 0.23%) and stromal MI was increased (control, 0.60%; progesterone, 2.1%). Thus, the measured effects on LI were indicative of altered proliferative activity of the tissues. These data demonstrate that uterine tissues of the neonatal mouse proliferate rapidly in the absence of gonadal steroids. Progestins and glucocorticoids specifically inhibit this estrogenindependent DNA synthesis of uterine epithelium.
ASJC Scopus subject areas