A comparison of the actions of stimulatory follicular fluid and gonadotropin-releasing hormone analogs on progesterone secretion by porcine granulosa cells.

Granulosa cells from small and medium porcine follicles (1-5 mm) were incubated with charcoal-treated follicular fluid from large (6-10 mm) follicles or porcine serum in the presence and absence of gonadotropin-releasing hormone (GnRH) analog and luteinizing hormone (LH) or follicle-stimulating hormone (FSH). A GnRH agonist inhibited follicular fluid's enhancement of basal and LH-stimulated progesterone secretion but did not block follicular fluid's enhancement of FSH-stimulated progesterone secretion. A GnRH antagonist mimicked follicular fluid's enhancement of basal and LH-stimulated progesterone secretion but did not mimic follicular fluid's action on FSH-stimulated progesterone secretion. When the GnRH antagonist and follicular fluid were added together, they acted synergistically in stimulating basal progesterone secretion, and were additive in enhancing LH-stimulated progesterone secretion. These observations suggest that separate follicular fluid molecules are responsible for its influence on LH and FSH actions on granulosa cells and that a GnRH-antagonist-like molecule could be responsible for some of follicular fluid's "luteinization stimulatory" action. Alternatively, the stimulatory follicular fluid molecule may not resemble GnRH but may act via a mechanism that is opposed by GnRH.