Response of follicle cells to ovulatory stimuli within the follicle and in primary culture

Cultures of mural granulosa cells (mGCs) and cumulus oocyte complexes (COCs) were employed to investigate various aspects of follicle cell function and response to gonadotropins. Yet, such studies do not reveal the intricate cell-to-cell interactions in the whole follicle. Here we compare the ovulatory responses to LH/hCG or epiregulin (ER) of rat preovulatory follicles and of mGC and COC whether they were stimulated within the follicle or in primary cell cultures.The expression of TSG-6 and COX-2 mRNA varied according to the culture system and mode of stimulation. In primary cultures stimulated with LH or ER resulted in their lower expression as compared to stimulation of follicles. LH/hCG stimulated higher follicular and mGC AR, ER and EGFR mRNA levels than in primary mGC cultures. COCs stimulated by LH/hCG in vivo responded with AR, ER and EGFR mRNA expression, but not in culture where only EGFR mRNA was stimulated. The differences in gene expression of mGCs and COCs when stimulated within their intact follicle or in primary cultures revealed here underscore the important role of cell–cell interactions in follicle physiology. Therefore, results obtained in primary mGC cultures need careful validation in models reproducing such in situ interactions for revealing mGC activity within the intact follicle.