Effect of Prostaglandins on Collagen Synthesis in Rabbit Ovarian Follicles during the Ovulatory Process

Abstract

Collagen fibers in the ovarian follicle undergo drastic changes at ovulation due to the preovulatory increase of collagenolytic activities. The collagen synthesis in ovaries, however, has not been elucidated yet. To clarify the regulatory role of prostaglandins (PGs) in collagen synthesis of the follicular wall in relation to the ovulatory process, we measured prolyl hydroxylase (PH), as well as lysyl oxidase (LO) activity and the content of hydroxyproline (Hyp) in ovarian follicles of the rabbits treated by hCG, hCG/indomethacin (IM) and hCG/ IM/various PGs. The experimental groups consisted of; 1) untreat control group 2) ovulatory group receiving hCG 3) non-ovulatory group given PGs 4) ovulatory group given hCG and PGs 5) group in which hCG-induced ovulation was inhibited by IM (4mg/kg) 6) group in which IM-inhibited ovulation was recovered by PGF_2α (1.5 mg/kg) 7) group in which IM-inhibited ovulation was not restored by PGE₁ (0.1mg/kg) and PGE₂ (0.7mg/kg). The peak activities of PH and LO in ovarian follicles were observed at 12-13 hr after hCG injection, namely, immediately after ovulation. Significant changes of these activities after hCG administration were specific to the ovaries. PH activity in the ovaries was sup-pressed by the administration of IM, but LO activity was not significantly suppressed.
In the hCG/IM/PGF_2α-treated ovulatory rabbits (Group 6), PH activity recovered to nearly the level of the hCG-treated rabbits (Group 2). By addition of PGE₂, ovulation did not recover but PH activity was restored to about 70% of the hCG-treated rabbits. PGE1 did not have any effect on the reversal of ovulation-blockage or restoration of PH activity.
The amount of Hyp after hCG administration tended to decrease from 6 hr to 10 hr but was significantly increased from 10 hr to 13 hr. This increase of Hyp after ovulation significantly correlated with the increase of PH and LO activities. In the hCG/IM/PGF_2α-treated rabbits (Group 6), the changes of Hyp were similar to those the hCG-treated rabbits (Group 2).
In conclusion, collagen synthetic activity, found to be regulated by PH and LO activities in the ovarian follicles, was activated after follicle rupture, resulting in reconstruction of collagen fibers, and PGs play an important role in the ovulatory process by modifying collagen synthesis.