Granulosa cells of the cumulus oophorus are different from mural granulosacells in their response to gonadotrophins and IGF-I

There are two types of granulosa cells: those which surround the oocyte are cumulus cells (CC) and those which surround the antrum are mural granulosa cells (MGC). These cells are under the influence of several hormones and g rowth factors, the most important of which are gonadotrophins and IGF-I. In this article, we report novel observations on the differences between thes e two types of granulosa cells and their interaction with gonadotrophins an d IGF-I. We were able to conduct physiological studies on the role of IGF-l by using an analogue of IGF-I which does not bind to IGF-I-binding protein s (LR3-IGF-I). Immature rats received saline, equine chorion-ic gonadotroph in (eCG), LR3-IGF-I or eCG plus LR3 -IGF-I by infusion using a pump from 24 -29 days of age. The rats were killed and the ovaries removed. Surface foll icles were punctured and MGC and oocyte cumulus complexes were removed. The se were cultured in saline (control) and in three different doses of FSH. C ell replication was assessed by H-3-thymidine incorporation and differentia tion was evaluated by the measurement of progesterone secretion. It was not ed that CC replicated ten times more than MGC. Similarly, progesterone secr etion by CC was six times more than by MGC. In vivo exposure to gonadotroph ins (eCG) positively influenced iii vitro treatment with FSH in both cell t ypes. This phenomenon was observed in both cell replication and progesteron e secretion. The IGF-I analogue had a positive effect on cell replication o f MGC but a negative effect on the cell replication of CC. With respect to progesterone secretion, the IGF-I analogue had a negative effect on CC but a positive effect on MGC. In conclusion, CC behaved differently from MGC in response to gonadotrophins and the IGF-I analogue. IGF-I and FSH acted add itively, synergistically or antagonistically in different circumstances.