Oxytocin-neurophysin I mRNA abundance in equine uterine endometrium

A positive-feedback loop between luteal oxytocin and uterine prostaglandin F-2 alpha (PGF) is a major signal for luteolysis in ruminants. Likewise, ut erine PGF Causes luteolysis in mares, but the involvement of oxytocin in th is process is unclear. We wanted: 1) to determine if the oxytocin-neurophys in I (OT-NP I) gene is transcribed into mRNA in the endometrium of mares; a nd, if so, 2) to analyze relative changes in abundance of endometrial OT-NP I mRNA throughout the estrous cycle and during early stages of pregnancy. Endometrial biopsies were obtained from nonbred mares during estrus, and 5, 10, and 15 d after ovulation (n = 3/d). Biopsies were also obtained from p regnant mares 10, 15, and 20 d after ovulation (n = 3/d). Relative amounts of OT-NP I and glyceraldehyde-3-phosphate dehydrogenase mRNA in endometrium were assessed by reverse transcription-polymerase chain reaction and South ern blotting. Endometrial OT-NP I mRNA abundance changed with day of the cy cle or pregnancy, and levels at estrus were higher than at any other days e xamined. The OT-NP I mRNA levels were negatively correlated with serum prog esterone across all days examined and positively correlated with serum estr adiol in nonbred mares. The reverse transcription-polymerase chain reaction products for both OT-NP I and glyceraldehyde-3-phosphate dehydrogenase wer e cloned into vectors and sequenced. Each shared greater than 89% nucleotid e and predicted amino acid identities with the respective human, bovine, ov ine, and rat products. Uterine oxytocin may be involved in regulation of re productive tract function during the estrous cycle and/or establishment of pregnancy in horses. (C) Elsevier Science Inc. 1999.