Temporal Expression of Prostaglandin H Synthase Type 2 (PGHS-2) and P450(C17)in Ovine Placentomes with the Natural Onset of Labour

Labour in the sheep is preceded by increased tissue and plasma prostaglandin (PG) concentrations, and PGs could potentially contribute to the regulation of P450(C17)in placental tissue. Therefore, we determined the cellular localization and temporal pattern of expression of P450(C17)and prostaglandin H synthase type 2 (PGHS-2), the primary PG synthetic enzyme, in intrauterine tissues from three groups of pregnant ewes at term; animals not in labour (NIL;n=5; 140-145 days of gestation), animals in early labour (EL;n=6; 143-149 days) and animals in active labour (L;n=6; 145-149 days). Allocation of animals into the three groups was based on continuous monitoring and assessment of myometrial contractile activity (EMG) and changes in the intrauterine pressure (IUP). Levels of mRNA encoding PGHS-2 and P450C17 were determined by in situ hybridization. Localization and levels of immunoreactive (ir-) P450(C17)and ir-PGHS-2 protein were determined by immunohistochemistry and Western blotting. PGHS-2 mRNA and ir-PGHS-2 were already elevated in placentomes of NIL animals and did not increase further with the progression of labour, whereas P450C17 mRNA increased progressively with labour, and ir-P450C17 rose significantly only in animals in active labour. The rise in P450C17 expression corresponded temporally to a progressive increase in maternal plasma concentration of oestradiol. We suggest that the temporal relationship and subsequent co-localization of PGHS-2 and P450(C17)proteins in the uninucleate trophoblast cells of the placentomes are consistent with the possibility that placental PGs could act to enhance placental output of oestrogen leading to labour and delivery.