FSH stimulates hyaluronic acid synthesis by oocyte–cumulus cell complexes from mouse preovulatory follicles

Abstract

A surge in the secretion of gonadotropins stimulates several processes in mammalian preovulatory follicles, including oocyte maturation, cumulus expansion (mucification) and ovulation. This surge results in increased circulating levels of both luteinising hormome (LH) and follicle-stimulating hormone (FSH). It has generally been thought that LH is primarily responsible for the stimulation of the maturational processes in preovulatory follicles that results in ovulation and corpus luteum formation, and that FSH stimulates the development of the next wave of preovulatory follicles. A direct role for FSH in preovulatory events has been unclear. However, two studies have suggested that FSH is essential for certain preovulatory processes. First, there is evidence that the production of plasminogen activator by granulose cells is more sensitive to FSH than to LH¹. Plasminogen activator could convert follicular fluid-borne plasminogen to plasmin, a protease capable of weakening the follicle wall². Second, highly purified FSH, but not highly purified LH, stimulates cumulus expansion by isolated mouse oocyte–cumulus cell complexes³. A critical step in cumulus expansion is the deposition of a hyaluronic acid matrix, so that the synthesis of this glycosaminoglycan is very important in the preparation of the mouse oocyte–cumulus cell complex for normal ovulation. I report here that the synthesis of hyaluronic acid in vitro is stimulated by FSH but not by LH.