Granulosa cells stimulate in vitro the expansion of isolated mouse cumuli oophori: involvement of prostaglandin E2

Granulosa cells (2 X 10(6) per ml) obtained from pregnant mare's serum gonadotropin (PMSG)-primed mice induce within 24 h the expansion in vitro of cocultured mouse cumuli oophori. Experiments with conditioned media showed that the expansion-promoting action of granulosa cells is due to diffusible factor(s) released into the culture medium. Studies with prostaglandin synthetase inhibitors and direct measurements of prostaglandin E2 (PGE2) released by granulosa cells in the culture medium have also been performed. The results strongly suggest that the cumulus oophorus expansion-promoting action of granulosa cells is mediated by PGE2, and support the hypothesis (Downs and Longo, 1983) that granulosa cells might play a similar role in the mechanism of cumulus expansion in vivo. The suggestion is advanced that coculture with granulosa cells might be of help to allow physiologic expansion in culture of immature cumuli obtained from preovulatory follicles in in vitro fertilization programs.