Effects of progesterone on expression of messenger RNA encoding oxytocin-neurophysin, oxytocin receptor and prostaglandin G/H synthase-1 and-2 duringthe early oestrous cycle in the ovine corpus luteum

This study was conducted to determine whether early progesterone treatment plays a role in the regulation of messenger RNA (mRNA) expression for oxyto cin-neurophysin, oxytocin receptor, prostaglandin G/H synthase (PGHS)-1 and PGHS-2 in the ovine corpus luteum. The expression of ovarian oxytocin, oxy tocin receptor, PGHS-1 and PGHS-2 mRNA was investigated in control, progest erone- or RU486-treated ewes. Fifteen ewes were randomly assigned to three groups to receive intramuscular injections of progesterone (12.5 mg; n = 5) , RU486, (2.5 mg kg(-1) bodyweight; n = 4) or corn oil(1 mL; n = 6) twice d aily from Day 1 to Day 3 post oestrus. On the morning of Day 4 post oestrus , the corpora lutea were collected and analysed for oxytocin-neurophysin mR NA by Northern blot using a labelled cDNA probe, and for the expressions of the oxytocin receptor, PGHS-1 and PGHS-2 mRNA using the reverse transcript ion polymerase chain reaction. Administration of progesterone or suppressio n of progesterone activity with RU486 did not affect expression of oxytocin -neurophysin mRNA (P>0.05). Pretreatment of the ewes with progesterone resu lted in the enhancement of luteal oxytocin receptor mRNA expression and sup pression of PGHS-1 and PGHS-2 mRNA (P<0,001). These results indicate that e arly progesterone treatment does not control the expression of oxytocin-neu rophysin mRNA in the ovine ovary but may be involved in the regulation of o varian oxytocin receptor and PGHS expression. It is proposed, on the basis of these results, that progesterone may play a role in premature corpus lut eum regression through an intra-ovarian mechanism involving the induction o f ovarian oxytocin receptor mRNA expression.