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 prostaglandi n (PG) concentrations, and PGs could potentially contribute to the regulati on of P450(C17) in placental tissue. Therefore, we determined the cellular localization and temporal pattern of expression of P450(C17) and prostaglan din H synthase type 2 (PGHS-2), the primary PG synthetic enzyme, in intraut erine tissues from three groups of pregnant elves at term; animals not in l abour (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 monito ring and assessment of myometrial contractile activity (EMG) and changes in the intrauterine pressure (IUP). Levels of mRNA encoding PGHS-2 and P450C1 7 were determined by in situ hybridization. Localization and levels of immu noreactive (ir-) P450(C17) and ir-PGHS-2 protein were determined by immunoh istochemistry and Western blotting. PGHS-2 mRNA and ir-PGHS-2 were already elevated in placentomes of NIL animals and did not increase further with th e 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 in crease 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 cons istent with the possibility that placental PGs could act to enhance placent al output of oestrogen leading to labour and delivery. (C) 2000 Harcourt Pu blishers Ltd.