Rapid estrogen metabolism and vitellogenin gene expression in Xenopus hepatocyte cultures

Male hepatocytes metabolized estradiol-17 beta, 17 alpha-ethinylestradiol and mestranol extremely rapidly (t 1/2 = 40, 60 and 300 min, respectively), whereas these were more stable in cultures of female hepatocytes (t 1/2 = 120, 150 and 640 min, respectively). Vitellogenin mRNA accumulated for only 12 h after a single addition of 10(-6) M estradiol to male hepatocyte cultures; mestranol, but not 17 alpha-ethinylestradiol or diethylstilbestrol, was more potent than the natural hormone. The level and rate of accumulation of vitellogenin mRNA were 5-15 times higher in female than in male hepatocytes, mestranol and estradiol being more potent than 17 alpha-ethinylestradiol and diethylstilbestrol. Ovariectomy, 60 days prior to cell culture, did not alter the metabolism of estradiol or the vitellogenic response of female hepatocytes. On the other hand, a single administration of estradiol in vivo to male Xenopus caused a long-lasting shift (at least 16 weeks) to the female pattern of its metabolism, although the enhanced inducibility of vitellogenin genes was partially reversed between 4 and 16 weeks after hormonal treatment. The addition of fresh estradiol every 4 h to male hepatocyte cultures to compensate for its rapid metabolism resulted in a continuous and sustained accumulation of vitellogenin mRNA at rates comparable to those attained in vivo. Our findings explain the requirement for high levels of estrogen to activate vitellogenin genes and establish Xenopus hepatocyte cultures as a reproducible system for analysing the expression of this multigene family.