Activation of the kinin system in the ovary during ovulation: Role of endogenous progesterone

BACKGROUND: Previous work by our group and others has implicated a role for kinins in the ovulatory process. The purpose of the present study was to elucidate whether endogenous progesterone, which is an intraovarian regulator of ovulation, might be responsible for induction of the kinin system in the ovary during ovulation. The gonadotropin-primed immature rat was used as the experimental model, and the role of endogenous progesterone was explored using the antiprogestin, RU486. RESULTS: The results of the study revealed that RU486 treatment, as expected, significantly attenuated ovulation. Activity of the kinin-generating enzyme, kallikrein, was elevated in the ovary in control animals prior to ovulation with peak values observed at 4 h post hCG, only to fall to low levels at 10 h, with a recovery at 20 h post hCG. RU486 treatment had no significant effect on ovarian kallikrein activity as compared to the control group. Total ovarian kininogen levels in control animals increased significantly at 12–14 h after hCG – coinciding with initiation of ovulation. Thereafter, ovarian kininogen levels fell to low levels at 20 h, only to show a rebound from 24–38 h post-hCG. RU486 treatment had no significant effect on the rise of total ovarian kininogen levels from 12–14 h after hCG; however, from 30–40 h post hCG, RU486-treated animals had significantly higher total ovarian kininogen levels versus control animals, suggesting that endogenous progesterone may act to restrain elevations of kininogens in the post-ovulatory ovary. This robust elevation of ovarian kininogen levels by RU486 was found to be primarily due to an increase in T-kininogen, which is a potent cysteine protease inhibitor. CONCLUSIONS: Taken as a whole, these results suggest that endogenous progesterone does not regulate kallikrein activity or kininogens prior to ovulation, but may provide a restraining effect on T-kininogen levels in the post-ovulatory ovary.