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Oocyte– Granulosa cell Interaction: Two- cell, Two- Gonadotropin System

المؤلف:  Wass, J. A. H., Arlt, W., & Semple, R. K. (Eds.).

المصدر:  Oxford Textbook of Endocrinology and Diabetes

الجزء والصفحة:  3rd edition , p1261

2026-10-24

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The next step after the awakening of a primordial follicle is formation of multilayer of granulosa cells surrounding the oocyte to form the preantral follicle stage (Figure1). While zona pellucida appears around the oocyte, the outer stroma modifies to theca cells. FSH receptors not only induce proliferation of granulosa cells but also act to induce the function of aromatase enzyme that converts androgens to oestrogens. Hence, local increase of oestrogen concentration steadily increases the number of FSH receptors on granulosa cells. Although low dose of androgens are essential as a precursor of aromatase activity and induction of the enzyme, high doses are associated with overproduction of 5- alpha androgens that in turn inhibit the enzyme activity and causes atresia.

Fig1. Phases and durations of follicular development.

As the layers of granulosa cells increase and fluid accumulation begins within a preantral follicle, the later stage of those follicles is designated as antral follicle. During this process, granulosa cells around the oocyte differ from the ones that cover the whole follicle with its functionality and called as cumulus oophorus. The content of the fluid within an antral follicle essentially consists of oestrogen and hence concentration of the steroids reflects the functional capacity of granulosa and theca cells within the context of two- cell, two- gonadotropin system. Insulin like growth factor- II produced in theca and granulosa cells also stimulate aromatase activity. One should also address that LH receptors are present only theca cells, and solely granulosa cells have FSH receptors. LH secretion is re sponsible for the production of androgens, namely androstenedione and testosterone which in turn metabolize to estrone and oestradiol with aromatase activity, respectively. Notably, inhibin induces and activin stimulates action of FSH, LH, and IGF- I. These findings might suggest that LH is also important for the late development of folliculogenesis and maturation. Nevertheless, within the context of selection of dominant follicle, a fall in FSH levels due to increased concentration of oestrogen decreases the aromatase activity and as sociated oestrogen synthesis. Impairment in granulosa cell will lead to a significant reduction in aromatase activity and cause more androgenic microenvironment and finally atresia. Briefly, containing the highest potency of aromatase activity and LH receptors with response to FSH appears to be the crucial factor for a given follicle in order to be attained as a dominant follicle in the later phase of the menstrual cycle.