Graafian follicle growth and replacement in anovulatory ovaries of ageing C57BL/6J mice

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Abstract
The growth of preantral follicles and replacement of large Graafian follicles were studied in reproductively senescent C57BL/6J mice immediately after the loss of estrous cyclicity when the ovary is approaching exhaustion of its follicular reserve. Granulosa cells were labeled in vivo by injection of 3H-thymidine and were evaluated by autoradiography. At 1 h after injection, labeling was confined almost exclusively to the cumulus and neighboring cells, whereas the distribution of labeled granulosa cells in preantral follicles was approximately uniform. The proportion of labeled mural cells in graafian follicles rose from initially low values to maximal levels 3 days later; apparently those follicles that were Graafian at the time of injection had been replaced by recruitment of preantral stages. The rate of growth of preantral follicles was similar in senescent anovulatory mice and in young adult animals. A simple model was constructed to illustrate how persistent vaginal cornification in aging mice is sustained by a stream of Graafian follicles, and why some of the latter did not respond fully to an ovulatory dose of hCG [human Chorionic gonadotropin].