ALTHOUGH the essential role of endocrine function of the fetal testis for male phenotypic development is established1-3, endocrine function of the fetal ovary is not thought to be essential for development of the female phenotype1. Furthermore, it has been generally assumed that the fetal ovary has little capacity for oestrogen synthesis until late in embryonic life4-9. However, we recently reported that the capacity of the embryonic ovary of rabbit and human to synthesise oestrogen from radioactive androgen develops at about the same time as the onset of the capacity for testosterone synthesis in the fetal testes of the same species and before the histological differentiation of the ovary10,11. To determine if this enzymatic capacity to synthesise oestrogens is actually indicative of oestrogen formation in the intact tissue, we have measured and report here the content of 17β-oestradiol and testosterone in embryonic gonads of the fetal rabbit at varying stages of development. The results indicate that the onset of formation of the characteristic steroid hormones takes place simultaneously in ovary and testis.
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