Inhibitory Effects of Prolactin in the Mechanism of Follicle Rupture in the in vitro Perfused Rabbit Ovary

Abstract

The present study was undertaken to assess the effects of prolactin (PRL) in the process of ovulation in the in vitro perfused rabbit ovary. The addition of PRL (10〜10^3ng/ml) to the perfusate inhibited hCG-induced ovulation in a dose-dependent manner. However, PRL did not affect hCG-stimulated prostaglandin (PG) F_2α and E_2 and leukotriene B_4 (LTB_4) production by the perfused rabbit ovaries. In the process of ovulation, ovarian ai plasmin inhibitor-plasmin complex (α_2PI-Plm) generation rate reached its maximal level at 4 hours after exposure to hCG and then declined. The second peaks occurred at 8h after hCG administration. Exposure to PRL at 10^3ng/ml significantly inhibited hCG-induced ca PI-Plm generation in ovaries throughout the entire perfusion periods. A significant positive correlation between the α_2PI-Plm generation rate at 4 hours after hCG administration and the ovulatory efficiency was observed. Furthermore, PRL inhibited hCG-stimulated intrafollicular α_2PI-Plm content at 4 hours after hCG administration in the perfused rabbit ovaries in a dose-dependent manner. In conclusion, PRL directly inhibits hCG-induced ovulation in the rabbit ovary, at least in part, by a mechanism depending upon inhibition of the plasmin generating system in the preovulatory follicles.