Direct induction by estradiol on vitellogenin synthesis in organ cultures of male Xenopus laevis liver.

Organ cultures of liver from untreated male Xenopus respond to 17 beta-estradiol in the culture medium by synthesizing and secreting the yolk protein precursor vitellogenin. Vitellogenin synthesis, as a primary response, is first detectable on the fourth day of culture, and comprises up to 12% of the protein synthesized on the eighth day. Estradiol is required during the lag period of 4 days. Tissue from male Xenopus injected with 1 mg of estradiol 30 days before the start of culture responds more rapidly and to a greater extent to estradiol in the medium than tissue from uninjected males. During such a secondary response, vitellogenin is first detectable in the medium on the second day of culture, and becomes up to 24% of the protein synthesized on day 6. The rate of amino acid incorporation into total protein also increases in response to estradiol, but the rate of synthesis of albumin decreases rapidly in culture whether or not estradiol is present, in both the primary and secondary responses. A maximal response is seen with 10(-8) M estradiol. Progesterone, testosterone, dexamethasone, and insulin neither induce vitellogenin synthesis in culture nor modify the response to estradiol. DNA synthesis inhibitors do not prevent the response to estradiol in vitro, suggesting that cell division is not required for the initial response leading to vitellogenin synthesis.