Expression of prostaglandin H synthase isoforms in human myometrium at parturition

OBJECTIVE: The purpose of this study was to identify the isoforms and splicing patterns of prostaglandin H synthase present in pregnant human lower-segment myometrium and determine whether there is differential expression of the isoforms or splice variants with respect to gestational age or parturition. STUDY DESIGN: Lower-segment myometrium was collected at cesarean section at term (>37 weeks) or preterm (<37 weeks) from patients who were or were not in labor. Total messenger ribonucleic acid was isolated and reverse transcribed. Polymerase chain reaction for prostaglandin H synthase isoforms 1 and 2 and calponin were performed. Primers designed to characterize the splicing patterns of exon 9 of prostaglandin H synthase-1 were used. RESULTS: The predominant polymerase chain reaction product in all samples corresponds to prostaglandin H synthase-1 messenger ribonucleic acid spliced to include exon 9, but a less-abundant polymerase chain reaction product corresponding to prostaglandin H synthase-1 messenger ribonucleic acid spliced at the internal donor site of exon 9 was also detected. Prostaglandin H synthase-2 messenger ribonucleic acid was detected in human myometrium at a lower abundance than prostaglandin H synthase-1, and neither prostaglandin H synthase-1 or prostaglandin H synthase-2 messenger ribonucleic acid expression changed significantly with gestational age or labor. CONCLUSION: Both prostaglandin H synthase-1 and prostaglandin H synthase-2 isoforms are present in human myometrium. The prostaglandin H synthase-1 messenger ribonucleic acid that includes all of exon 9 encodes the predominant prostaglandin H synthase-1 isoform present in human myometrium. No significant alterations in the expression or splicing patterns for prostaglandin H synthase-1 were detected with respect to gestational age or the onset of labor; but prostaglandin H synthase-1 expression appeared higher at term in anticipation of labor. Although prostaglandin H synthase-2 is present in human myometrium, induction of prostaglandin H synthase-2 does not occur in lower-segment myometrium at parturition.