Estrogen-independent growth of mouse vaginal epithelium in organ culture

A serum-free vaginal explant culture system was established to investigate the in vitro effect of estrogen on the growth of mouse vaginal epithelium. Vaginal explants were isolated from 40-day-old, ovariectomized BALB/cCrgl mice and cultured in a basal unsupplemented medium or in basal medium plus various doses of 17 beta-estradiol. Explants were processed for histology at the end of culture periods or were given 4-hour pulses of tritiated thymidine at various times and processed for autoradiography. Vaginal epithelium increased 3- to 5-fold in thickness and 2-fold in the number of epithelial cell layers during 72 hours of culture without estrogen; addition of estrogen did not significantly influence epithelial growth. Keratinization of vaginal epithelium occurred within 48 hours of culture in the absence of estrogen, and again addition of estrogen did not accelerate its appearance. Covering the explants with collagen decreased the estrogen-independent growth of vaginal epithelium. Autoradiography showed that ca. 70-90% of basal epithelial cells entered S phase during the initial 4 hours of culture and that this number declined rapidly after 48 hours to ca. 20%. Addition of 1.8 nM 17 beta-estradiol significantly decreased the labelling index of basal cells at 48 hours, but did not affect the labelling index at 24 and 72 hours. Stromal cells were not labelled at any time. Thus, DNA synthesis, cellular proliferation, and differentiation (keratinization) of vaginal epithelium in organ culture occurred without estrogen and were not stimulated by the addition of estrogen.