Effect of exogenous gonadal steroids and pregnancy on uterine luminal prostaglandin F in mares.

The study examines how external hormone treatment and pregnancy affect levels of prostaglandin F (PGF) in the uterus of mares. It found an increase in uterine PGF levels due to exogenous progesterone, while pregnancy led to a reduction.

Objective and Methodology of the Study

• The study was designed to explore the effect of hormone treatment on uterine prostaglandin F (PGF) in mares. There were two main laboratory experiments conducted and analysed.
• In the first experiment, ponies without ovaries were treated with different hormonal substances. The treatment groups consisted of mares treated with corn oil, estradiol valerate, progesterone, or estradiol valerate followed by progesterone.
• In the second experiment, uterine fluid was collected from horse mares with removed ovaries prior to hormone treatment and post-treatment. The hormone therapy comprised of two phases: phase one entailed a treatment of estradiol valerate and phase two consisted of progesterone treatment. The duration of the therapy was 57 days in total.
• In a third experiment, PGF was measured in uterine fluid of pony mares at various points (days 8, 12, 14, 16, 18, 20) of the estrous cycle and pregnancy.

Results of the Study

• The results of the experiments showed that progesterone considerably increased the level of uterine luminal PGF in comparison to all other groups which did not show significant differences among themselves.
• The second experiment noted that uterine PGF levels were significantly lower prior to the treatment as opposed to after the treatment.
• Results from the third experiment revealed that a significant day effect was observed in non-pregnant mares where PGF level increased in the late luteal phase and declined thereafter. A day effect was not observed in pregnant animals and prostaglandin levels in their uterine luminal were lower than those not pregnant.

Conclusion of the Study

• The study concludes that the administration of exogenous progesterone leads to an increased level of PGF in the uterus.
• It also establishes that pregnancy suppresses the level of PGF in the uterus, which contradicts the ability of the endometrium of mares to produce high levels of PGF.
• The researchers hypothesize that the presence of a conceptus (the embryo and associated membranes) may inhibit synthesis or release of PGF, thereby allowing for luteal maintenance (supporting the corpus luteum which is a temporary endocrine structure involved in ovulation and early pregnancy).