[Granulosa-cell growth factor in oocyte and its transport systems]

The possible existence of granulosa-cell growth factor (GGF) in the oocyte has been investigated using the labelling index (LI) with 3H-Thymidine and the mitotic index (MI) of granulosa cells (G-cells) in mice. The following results were obtained. In preantral follicles the LI increased with the development of the oocyte until its diameter reached the maximum (approximately 90 mu). In preantral follicles with the oocyte diameter below 69 mu, the LI was low and the follicular diameter was small. As the oocyte developed, the LI increased and reached the maximum value when the follicular diameter was approximately 200 mu. Then it decreased a little but maintained a high value. The antrum formation was seen when the follicular diameter was about 300 mu showing no change in LI. In preantral follicles with the oocyte diameter over 80 mu the G-cell near the oocyte had a much higher LI than the distant one. After the antrum formation, the LI and MI of cumulus layers adjacent to the oocyte were three times as great as those of the mural layers. Among the mural cell layers in the antral follicle the layer adjacent to the antrum showed remarkably high LI in comparison with the distant layers. These results suggest that GGF which seems to play a role in the formation of cumulus is secreted with the development of the oocyte. The GGF is transported through two systems the preantral follicle and cumulus layer through the G-cell gap junction and mural layers through the follicular fluid.