Effects of steroids on endometrial oxytocin mRNA production

In this study, the roles of oestrogen and progesterone in the regulation of oxytocin gene expression in equine endometrium were examined. Anoestrous mares (n=19) were assigned randomly to one of the following treatment groups: control (vehicle control for 1 day; n=3); progesterone (250 mg progesterone per day for 6 days; n=4); oestradiol (5 mg beta-oestradiol 17-valerate per day for 6 days; n=4); oestradiol plus short duration progesterone (5 mg beta-oestradiol 17-valerate per day for 6 days followed by 250 mg progesterone per day for 6 days; n=4); and oestradiol plus long duration progesterone (5 mg beta-oestradiol 17-valerate per day for 6 days followed by 250 mg progesterone per day for 12 days; n=4). Jugular venous blood samples were obtained for oestrogen and progesterone radioimmunoassays. Endometrial biopsies were obtained and total RNA was extracted. Expression of mRNA for oxytocin and glyceraldehyde 3'-phosphate dehydrogenase was assessed by RT-PCR and Southern blotting. Oxytocin mRNA abundance was significantly higher (P < 0.05) in the oestrogen-treated group than in all other groups. These data demonstrate that oestradiol priming for 6 days upregulated expression of the endometrial oxytocin gene. Progesterone treatment for either 6 or 12 days after oestradiol priming returned oxytocin mRNA abundance to levels similar to those of controls.