Patterns of [3H] thymidine incorporation differ in immature rats and mature, cycling rats

By the time follicular development has progressed to the preovulatory stage, granulosa cells abutting the basement membrane no longer incorporate [3H] thymidine (3H-TdR). The purpose of this experiment was to determine when, during the course of follicular growth, cell proliferation in these mural granulosa cells ceases. Autoradiographs were prepared following continuous 3H-TdR infusion in vivo, or incubation with 3H-TdR in vitro. In cycling rats, the concentration of silver grains over mural regions of the granulosa layer was lower than over antral regions of most follicles with greater than 1000 cells in the largest cross section (LCS). This centripetal labeling pattern became more striking as follicular size increased. By proestrus, only the cells of the discus proligerus (cumulus and the portion of the follicular wall supporting the cumulus oocyte complex) continued to incorporate 3H-TdR. In contrast to cycling rats, centripetal labeling patterns were not seen in ovaries of prepubertal rats, even in follicles of the same size. The difference in follicular growth patterns between these two types of animals suggests an influence of cyclic gonadotropin surges on the control of granulosa cell proliferation.