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In vitro studies on differentiation of the reproductive tract.

This paper will summarize some of the results of a series of organ-culture studies on sex differentiation of the reproductive tract of foetal guinea-pigs. Three aspects will be discussed: (1) the the secretory activity of the gonads in relation to the chronological steps in morphogenesis of the gonads and the reproductive ducts (Wolffian and M ullerian); (2) the dependence of the Wolffian ducts on testicular hormones at the critical period of development; (3) the marked independence of the Mullerian ducts from ovarian-secreted hormones. A culture method was selected for this study because organs or reproductive tracts can be isolated from the complex foetal environment as explants and maintained in culture under controlled conditions, thus avoiding many complications encountered in experimentation in vivo . The explantation and culture of isolated reproductive tracts of foetal rats and mice have been successful (see review by Price & Ortiz 1965) and essentially the same method that was used in these earlier studies has been employed for the guinea-pig, except for some important modifications. The technique is basically a watch-glass method in which a natural medium is used. A detailed description was given in Zaaijer, Price & Ortiz (1966) and Price, Ortiz & Zaaijer (1967). The guinea-pig is a favourable species for such experimentation because it is a long-term rodent (average gestation period 68 days) and the morphogenetic changes involved in sex differentiation of the reproductive ducts in vivo extend from 29 to 38 days of foetal life. The stages and timing in sex differentiation in vitro were found to be closely similar to those in vivo . This protracted period of 9 days was advantageous for close study i n vitro of the steps in maintenance and development of the ducts or, conversely, in their retrogression and degeneration under various hormonal conditions. Such a study was greatly facilitated by the visibility of the ducts in the explants during the culture period.