Endogenous prostaglandin F2α release induced by physiologic saline solution infusion in utero in the mare: Effect of temperature, osmolarity, and pH

SUMMARY Thirty mares with normal estrous cycles were allotted equally to 5 groups and infused with 250 ml of saline (NaCl) solution in utero on the seventh day after ovulation to test the effects of temperature, osmolarity, or pH of the saline solution on prostaglandin F2α (pgf2α) release and luteolysis. Intrauterine infusion of phosphate-buffered saline solution failed to alter the duration of the luteal phase, compared with the control group. Similarly, increasing the temperature of phosphate-buffered saline solution to 42 C or increasing (600 mosm) or decreasing osmolarity (< 10 mosm) did not change the duration of the luteal phase. Decreasing the pH of saline solution to 3 caused significant (P < 0.0001) releases of pgf2α from the uterus within the first hour after infusion, and the luteal phase was shortened to 8.8 ± 1.0 days (mean ± sem; control, 15 ± 1.2 days). The results of this study showed that pH is the main factor in eliciting pgf2α release by intrauterine infusion of a saline solution, whereas increased temperature and osmolarity have no effect on the release of pgf2α.