Interleukin-1-Mediated Regulation of Plasminogen Activation in Pregnant Mare Serum Gonadotropin-Primed Rat Granulosa Cells Is Independent of Prostaglandin Production

Abstract

Objectives: This study examines the effects of interleukin-1 (IL-1) on plasminogen activator (PA) activity and prostaglandin (PG) E production in pregnant mare serum gonadotropin (PMSG)-primed granulosa cells and the potential involvement of PGE in the regulation of ovarian plasminogen activation.

Methods: Granulosa cells were obtained from PMSG-primed rat (27-day-old) ovaries and cultured in serum-free conditions for 48 hours in the absence or presence of IL-1β (10 ng/mL) with and without transforming growth factor-β1 (10 ng/mL). Cellular PA activity was measured through the conversion of plasminogen to plasmin and assay of the plasmin-mediated cleavage of [¹⁴C]-labeled globin to acid-soluble products.

Results: Exposure of PMSG-primed granulosa cells to IL-1 resulted in a 30% reduction (P < .05) in PA activity. Addition of hCG (1 IU/mL) to the granulosa cell cultures resulted in a 2.3-fold increase in PA activity, an effect significantly attenuated by co-administration of IL-1. The IL-1-mediated inhibition occurred concurrent with a 6.6-fold increase in the ability of the corresponding conditioned media to inhibit exogenous urokinase activity. This latter inhibitory capacity was the result of a significant increase in plasminogen activator inhibitor type 1 (PAI-1), given its abolition by a polyclonal anti-rat PAI-1 immunoglobulin G. The IL-1-mediated effects on PA/PAI-1 were accompanied by a sevenfold increase in PGE content of the spent culture medium. This response was dose dependent. The IL-1 effects on plasminogen activation and PG production were abolished by the IL-1 receptor antagonist, suggesting specific IL-1 receptor-mediated responses. Indomethacin, an inhibitor of PG biosynthesis, prevented the IL-1-induced increase in PGE accumulation but failed to affect the response of the PA system. Transforming growth factor-β1, a known regulator of IL-1 action, significantly attenuated the IL-1-stimulated PGE production but did not interfere with the ability of IL-1 to affect the PA system.

Conclusion: The present observations suggest a pleiotropic response of PMSG-primed granulosa cells to IL-1, characterized by the induction of PAI-1 concurrent with but independent of PG production. These findings corroborate and extend earlier observations suggesting that IL-1 affects PA activity and PGE production in immature rat ovaries. Moreover, these observations support our contention that IL-1 may play a major regulatory role in the cellular events leading to ovulation and early corpus luteum formation.