Abstract
Despite their importance in mammalian reproduction, substances in the oxytocin-prostaglandins pathways have not been investigated in the horse placenta during most of pregnancy and parturition. Therefore, we quantified placental content of oxytocin (OXT), oxytocin receptor (OXTR), and prostaglandin E2 and F2 alpha during days 90–240 of pregnancy (PREG), physiological parturition (PHYS), and parturition with fetal membrane retention (FMR) in heavy draft horses (PREG = 13, PHYS = 11, FMR = 10). We also quantified OXTR and prostaglandin endoperoxide synthase-2 (PTGS2) mRNA expression and determined the immunolocalization of OXT, OXTR, and PTGS2. For relative quantification of OXT and OXTR, we used western blotting with densitometry. To quantify the prostaglandins, we used enzyme immunoassays. For relative quantification of OXTR and PTGS2, we used RT-qPCR. For immunolocalization of OXT, OXTR, and PTGS2, we used immunohistochemistry. We found that OXT was present in cells of the allantochorion and endometrium in all groups. PTGS2 expression in the allantochorion was 14.7-fold lower in FMR than in PHYS (p = 0.007). These results suggest that OXT is synthesized in the horse placenta. As PTGS2 synthesis is induced by inflammation, they also suggest that FMR in heavy draft horses may be associated with dysregulation of inflammatory processes.
Highlights
Despite their importance in mammalian reproduction, substances in the oxytocin-prostaglandins pathways have not been investigated in the horse placenta during most of pregnancy and parturition
prostaglandin endoperoxide synthase-2 (PTGS2) synthesis is induced by inflammation[29,30,31,32,33,34], and during pregnancy in the horse, its synthesis should be suppressed by high levels of progestagens, as it is suppressed by high levels of progesterone in other species[35]
Mean OXT content was higher in fetal membrane retention (FMR) than in physiological parturition in both tissues, but the differences were not statistically significant (allantochorion: 3.7-fold, 95% confidence interval for the fold-change (CI) = −1.9 to 27.0-fold, p = 0.44; endometrium: 1.2-fold, CI = −30.1 to 41.1-fold, p = 0.92) (Fig. 1b)
Summary
Despite their importance in mammalian reproduction, substances in the oxytocin-prostaglandins pathways have not been investigated in the horse placenta during most of pregnancy and parturition. We quantified placental content of oxytocin (OXT), oxytocin receptor (OXTR), and prostaglandin E2 and F2 alpha during days 90–240 of pregnancy (PREG), physiological parturition (PHYS), and parturition with fetal membrane retention (FMR) in heavy draft horses (PREG = 13, PHYS = 11, FMR = 10). PTGS2 expression in the allantochorion was 14.7-fold lower in FMR than in PHYS (p = 0.007) These results suggest that OXT is synthesized in the horse placenta. It seems likely that horse placental OXT would be a signal for prostaglandin release in the placenta itself, and not a signal for myometrial contractions. Neither PTGS2 enzyme nor PTGS2 mRNA have been quantified in the horse placenta after day 22 of pregnancy or at parturition
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