Prostaglandins and the regulation of parturition in mares

Abstract

Prostaglandins play an essential role during the perinatal period in the mare. Prostaglandin concentrations are low for the majority of pregnancy due to the regulatory action of progestagens on those enzymes responsible for metabolism of prostaglandins. Towards term, prostaglandin concentrations gradually increase, closely associated with upregulation of the fetal hypothalamo-pituitary-adrenal axis, stimulation of the prostaglandin synthesising enzyme PGHS-2 and changes in the ratio of progestagens and oestrogens. Recent evidence in the mare indicates that proinflammatory cytokines are key mediators of prostaglandin synthesis both at term parturition in healthy mares and at preterm parturition associated with placental infection. Prostaglandin concentrations rise substantially during active labour and decline after birth, associated with delivery of the placenta. During induced labour, prostaglandin concentrations are variable depending on the proximity to spontaneous parturition at term. Once the proinflammatory endocrine cascade is initiated, it is difficult to prevent active labour by administration of drugs that reduce prostaglandin concentrations in peripheral plasma. Further work is needed to establish the inter-relationships between prostaglandin production and other endocrine changes associated with labour at term and preterm in the mare.

Giraffe birth locations in the South Luangwa National Park, Zambia: site fidelity or microhabitat selection?

“…Birth site location is probably not only dependent upon ecological factors, but reflects female physiological state. A common cascade of endocrine interactions tends to precede parturition, although the specific nuances differ across species (Kamel, ; Ousey & Fowden, ; Shenavai et al ., ). In general, the primary stimulus to birth derives from the foetus, not the mother.…”

A racing start in life? The hurdles of equine feto‐placental pathology

“…The influence of inflammatory mediators, cardiovascular/cord compromise, hypoxia and other disease processes are poorly documented in horses, but may have interesting correlations with human perinatal disease and are discussed further in other reviews in this supplement Fowden et al . 2012; (Ousey and Fowden 2012).…”

The oxytocin-prostaglandins pathways in the horse (Equus caballus) placenta during pregnancy, physiological parturition, and parturition with fetal membrane retention

“…PTGS2 is the predominant isoform in human, bovine, and ovine placentas 18,19,28 . 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 . Similarly, it seems likely that PTGS2 synthesis would be upregulated at parturition in the horse, as it is in other species.…”

“…During pregnancy and parturition, PGE 2 and PGF 2α are synthesized by the placenta 35,36 and immediately secreted 28 . In epitheliochorial placentas, like that of the mare, they are believed to be synthesized mostly in the allantochorion and quickly degraded in the endometrium 35 . Both prostaglandins are released to placental fluids, but only small quantities are released to maternal peripheral blood 35 .…”

“…In epitheliochorial placentas, like that of the mare, they are believed to be synthesized mostly in the allantochorion and quickly degraded in the endometrium 35 . Both prostaglandins are released to placental fluids, but only small quantities are released to maternal peripheral blood 35 . Thus, for better insight into pregnancy and parturition in horses, it would be helpful to directly measure the content of PGE 2 and PGF 2α in the placenta.…”