Porcine granulosa cells produce a progesterone secretion inhibitory activity.

OBJECTIVE To extend our previous observations of granulosa cell conditioned medium inhibition on basal and FSH-stimulated progesterone secretion by granulosa cells from large porcine antral follicles. METHODS Granulosa cell conditioned media (SGCCM) were obtained from cultures of granulosa cells which were harvested from small porcine antral follicles. SGCCM were fractionated by filtration through an Amicon XM-50 and an PM-10 membrane. RESULTS Two fractions - XM-50 filtrate (<50 kDa) and PM-10 retentate (10-50 kDa) - exhibited well expressed inhibitory effect on the progesterone secretion from large follicle granulosa cells in vitro. Such inhibitory effect was fully prevented by heat treatment, partially inactivated by trypsin digestion (P<0.05), but was resistant to several freeze-thaw cycles and storage at -20 or -70 degrees C for up to one year. CONCLUSIONS It is suggested that SGCCM contains some regulatory substance(s) capable of inhibiting progesterone secretion by cultured granulosa cells and that the molecular weight of such substance is presumably between 10-50 kDa.