Expression of enzymes of cyclooxygenase pathway and secretion of prostaglandin E 2 and F 2α by porcine myometrium during luteolysis and early pregnancy

Abstract

Past studies of uterine prostaglandin (PGs) and pig reproduction have focused on endometrial rather than myometrial PGs. This study documents the synthesis and secretion of myometrial prostaglandins (PGs) in pigs and the involvement of oxytocin (OT) in these processes. Cyclooxygenase-2 (COX-2) expression was similar in myometrial explants from cyclic and pregnant pigs (days 14–16) and OT (10 −7 M) in vitro significantly increased COX-2 protein regardless of reproductive state. Basal expression of prostaglandin E 2 synthase (PGES) was higher during pregnancy than during luteolysis. Conversely, prostaglandin F synthase (PGFS) was highest during luteolysis and lower in myometrium from gravid animals. OT had no influence on the expression of PGES and PGFS. In another tissue culture experiment, myometrial slices produced more PGE 2 than PGF 2α regardless of reproductive state of the female. OT stimulated PGE 2 production in myometrium harvested during luteolysis and increased PGF 2α production in all tissues examined. Progesterone (P 4; 10 −5 M) blocked stimulatory effect of OT on myometrial PG release. Myometrial OTr mRNA was higher ( P = 0.03) during luteolysis than during pregnancy. In conclusion: (1) oxytocin increases myometrial COX-2 expression, but does not influence the expression of terminal enzymes of PGs synthesis (PGES and PGFS); (2) porcine myometrium preferentially produces PGs during early pregnancy and secretes more PGE 2 than PGF 2α; (3) myometrial OT and OTr support secretion of PGs from myometrium during luteolysis.