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Possible involvement of protein kinase C in gonadotropin-induced ovulation in the rat ovary
T Shimamoto1, M Yamoto, R Nakano
1Department of Obstetrics and Gynecology, Wakayama Medical College, Japan.
Abstract:
Recent reports indicate that protein kinase C may play an important role in the process of gonadotropin-induced ovulation in the ovary. In the present study, we examined the effect of the protein kinase C inhibitor, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), on LH-stimulated tissue type plasminogen activator (tPA) activity in cultured rat granulosa cells. Granulosa cells were obtained from PMSG-treated rats and cultured for 48 h in the presence or absence of H-7 (0.1-60 microM) with ovine LH (30 ng/ml), phorbol 12-myristate 13-acetate (10(-8) M), phorbol 12,13-dibutyrate (10(-8) M), or (Bu)2cAMP (5 mM). After culture, tPA activity in the conditioned medium was assayed by fibrin autography technique after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. H-7 (1.0-60 microM) inhibited LH-, phorbol 12-myristate 13-acetate-, or phorbol 12,13-dibutyrate-stimulated tPA activity dose dependently, and each ID50 was approximately 8 microM. However, H-7 did not inhibit (Bu)2cAMP-stimulated tPA activity. To investigate the effect of H-7 on the ovulatory process in vivo, PMSG-treated immature rats were injected with H-7 (10(-9)-10(-3) M) into the unilateral ovarian bursa just before human CG administration. After 24 h, the number of oocyte-cumulus complexes in the oviduct was counted. H-7 suppressed the number of oocytes released from treated ovaries dose-dependently. The light microscopical observation revealed that ovaries treated with H-7 contained a few corpora lutea and many large unruptured follicles. The results of the present study suggest that the suppressive effects of H-7 on human CG-induced ovulation might be partly due to the inhibition of tPA secretion by rat granulosa cells via protein kinase C inhibition.
Insights
Protein kinase C inhibition by H-7 suppressed ovulation in rats by reducing tissue plasminogen activator (tPA) activity in granulosa cells. This study highlights protein kinase C
Area of Science:
- Reproductive Biology
- Endocrinology
- Cell Signaling
Background:
- Protein kinase C (PKC) is implicated in gonadotropin-induced ovulation.
- Tissue type plasminogen activator (tPA) is crucial for ovulation.
- The role of PKC in regulating tPA during ovulation requires further elucidation.
Purpose of the Study:
- To investigate the effect of the PKC inhibitor H-7 on LH-stimulated tPA activity in rat granulosa cells.
- To determine the in vivo impact of H-7 on ovulation and follicular development in rats.
Main Methods:
- Cultured rat granulosa cells were treated with H-7, LH, phorbol esters, or (Bu)2cAMP.
- tPA activity was measured using fibrin autography after SDS-PAGE.
- In vivo, H-7 was administered to the ovarian bursa of PMSG-treated rats before hCG injection, and oocyte release was assessed.
Main Results:
- H-7 dose-dependently inhibited LH-, phorbol 12-myristate 13-acetate-, and phorbol 12,13-dibutyrate-stimulated tPA activity in granulosa cells (ID50 ≈ 8 μM).
- H-7 did not affect (Bu)2cAMP-stimulated tPA activity, suggesting a PKC-dependent mechanism.
- In vivo, H-7 suppressed hCG-induced ovulation and resulted in unruptured follicles, indicating impaired ovulatory processes.
Conclusions:
- PKC signaling is involved in the regulation of tPA secretion in rat granulosa cells.
- Inhibition of PKC by H-7 disrupts ovulation, partly through reduced tPA activity.
- PKC and tPA represent potential targets for modulating ovulation.