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

Abstract

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 growth factors, the most important of which are gonadotrophins and IGF-I. In this article, we report novel observations on the differences between these two types of granulosa cells and their interaction with gonadotrophins and IGF-I. We were able to conduct physiological studies on the role of IGF-I by using an analogue of IGF-I which does not bind to IGF-I-binding proteins (LR3-IGF-I). Immature rats received saline, equine chorionic gonadotrophin (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 follicles were punctured and MGC and oocyte cumulus complexes were removed. These were cultured in saline (control) and in three different doses of FSH. Cell replication was assessed by 3H-thymidine incorporation and differentiation was evaluated by the measurement of progesterone secretion. It was noted that CC replicated ten times more than MGC. Similarly, progesterone secretion by CC was six times more than by MGC. In vivo exposure to gonadotrophins (eCG) positively influenced in vitro treatment with FSH in both cell types. This phenomenon was observed in both cell replication and progesterone secretion. The IGF-I analogue had a positive effect on cell replication of 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 additively, synergistically or antagonistically in different circumstances.