Fetal thymus and thymuline stimulate the in vitro proliferation of oogonia in the fetal rat ovary]

In rat ovaries explanted on day 13.5 p.c. and cultured in vitro for up to 6 days, the number of germ cells is enhanced in thymulin-supplemented medium and/or after co-culture of the ovarian explants with foetal thymic tissue compared to ovaries cultured in synthetic medium. Corticosterone added to the medium prevents the secretion of thymulin by the foetal thymus and in that condition the thymus does not influence the proliferation of oogonia. These results provide additional evidence that the pituitary-adrenal-thymic axis might be involved in the control of oogonia proliferation in vivo, taking into account our previous experimental finding that the number of germ cells is increased in ovaries of hypophysectomized foetuses.