Stimulatory effects of bradykinin on the ovulatory process in the in vitro-perfused rat ovary

Abstract

The role of bradykinin in the ovulatory process was investigated using an in vitro-perfused rat ovary model. Stimulation with LH (0.1 μg/ml) resulted in 2.6 ± 0.5 (mean ± SEM) ovulations per ovary, whereas no ovulations occurred in the nonstimulated control group. Bradykinin (5 μM) added to the perfusion system hourly for 10 h induced 2 of 5 ovaries to ovulate, with 2 and 3 ovulations, respectively. When bradykinin (5 μM) was given as a single dose at 5 or 10 h after LH, the ovulation rate was significantly increased to 11.0 ± 2.8 and 8.6 ± 2.0 ovulations per ovary, respectively. A competitive bradykinin antagonist, phenylalanine bradykinin, inhibited the bradykinin-induced increase in LH-stimulated ovulations. The addition of LH, but not of bradykinin, increased the levels of prostaglandin endoperoxide synthase in granulosa cells, but the levels of the enzyme in the residual ovarian tissue were negligible. In contrast, prostacyclin synthase was predominantly located in the residual ovarian tissue. This enzyme was not affected by LH or bradykinin. LH increased the tissue levels of prostaglandins, predominantly prostaglandin E2 (PGE2), at 7 h, whereas the stimulatory effect of bradykinin was smaller, with a preferential increase in prostacyclin (prostaglandin I2) levels. This study indicates a modulatory role of bradykinin, possibly involving prostacyclin late in the ovulatory process, in the rat.