Physiological peripubertal activation of the ovary is not reproduced by pregnant mare serum gonadotropin (PMSG) administration.

The research aims to understand the effects of a hormone called Pregnant Mare Serum Gonadotropin (PMSG) on the physiological activation of rat ovary during puberty. It concludes that the use of PMSG may elevate the levels of estrogen and androgens but not progesterone, thus failing to replicate the natural peripubertal activation.

Objective of the Research

• The primary aim of this research was to examine the effects of pregnant mare serum gonadotropin (PMSG) on the hormone production in rat ovaries, particularly during the days leading up to the first ovulation.

Experimental Observations

• During the days preceding first ovulation, a rat ovary shows an increase in the release of estradiol (E2) and progesterone (P) in response to gonadotropins, which are hormones that stimulate the ovaries. There was however no significant increase in the androgens (A, testosterone + dihydrotestosterone).
• When juvenile 29-day-old rats were administered with PMSG, the in vitro response to human chorionic gonadotropin (hCG) in terms of E2 and A production was considerably increased after 2 days. The increase was notably larger than the results from juvenile or first proestrus stage rats.
• Conversely, the P response to hCG was not enhanced by PMSG. The results were similar to those of juvenile stage animals and significantly less than that of first proestrus stage rats.

Conclusion

• The research concluded that PMSG enhances the E2 and A response of immature ovaries to hCG but not the P response.
• The diminished P response was not found to be due to a greater conversion of P to its less active metabolite 20 alpha-hydroxy-4-pregnen-3-one (20 alpha-OH-P).
• The overall findings suggest that whilst PMSG treatment of immature rats may be a good model for studying E2 release from preovulatory ovaries, it does not replicate the entirety of the developmental changes associated with normal puberty.