Increased prostaglandin (PG) production within the uterine compartment has a pivotal role in the processes leading to labor onset in women. Two PG endoperoxide-H synthase (PGHS) isoenzymes have been identified in a number of cell types. PGHS-1 is constitutively expressed in most cases, whereas PGHS-2 expression is rapidly induced by several agonists. The aims of this study were to determine the levels of PGHS-1 and PGHS-2 expression before and after spontaneous labor (SL) onset in the amnion and to assess the contribution of PGHS-1 and PGHS-2 to enzyme activity. We established and validated ribonuclease protection assays to quantify PGHS-1 and PGHS-2 messenger ribonucleic acid (mRNA) levels in the amnion. PGHS enzyme activity was measured with an established assay. The antisense RNA probes used in the protection assays were generated using human PGHS-1 and PGHS-2 complementary DNAs. These probes specifically detected the 2.8-kilobase mRNA of PGHS-1 and the 4.8-kilobase mRNA of PGHS-2 in amnion RNA samples on Northern blots. We measured mRNA levels in amnion from patients after SL at term and from patients not in labor undergoing elective cesarean section (CS) at term. PGHS-2 mRNA levels were markedly higher after SL compared to levels in CS amnion [5.18 +/- 1.08 (n = 16) and 2.27 +/- 0.50 (n = 15), densitometric units, respectively; P < 0.02], whereas there was no difference in PGHS-1 mRNA levels after labor compared with CS samples. PGHS-2 mRNA levels were also positively correlated with PGHS enzyme activity in 4 separate assays with a total of 25 patients (r = 0.65-0.88; P < 0.05). There was no correlation between PGHS-1 mRNA levels and enzyme activity. We conclude that PGHS-2 mRNA is present in human amnion; its levels are elevated after SL onset, and they are correlated with enzyme activity. The stimulation of PGHS activity at labor onset probably involves increased expression of PGHS-2. The expression of PGHS-1 does not change in association with labor in human amnion.
Amnion Blotting, Northern