Prostaglandin endoperoxide H synthase-1 and -2 mRNA levels and enzyme activity in human decidua at term labor.

Objective: To determine the labor-related changes of prostaglandin endoperoxide H synthase (PGHS) activity and PGHS-1 and -2 abundance in term decidua and to assess the contribution of the PGHS isoforms to the total PGHS activity present in the tissue.
Methods: Decidua was collected after elective cesarean delivery (CD) or spontaneous labor (SL) at term. Prostaglandin endoperoxide H synthase activity was determined in microsomal fractions, and PGHS-1 and -2 mRNA levels were measured by ribonuclease protection assays. Prostaglandin endoperoxide H synthase-1 and -2 mRNAs were localized in tissue sections by in situ hybridization.
Results: Prostaglandin endoperoxide H synthase specific activity in decidua microsomes at CD was 111 +/- 3 pg prostaglandin-E2/minute/microgram protein (mean +/- standard error, N = 10 patients), not different from enzyme activity measured after SL (110 +/- 27 N = 10 patients, P = .97, Wilcoxon's rank sum test). Prostaglandin endoperoxide H synthase-1 mRNA abundance in CD tissues was 0.283 +/- 0.047 relative densitometric units (mean +/- standard error, n = 26 patients), which did not change with labor (SL: 0.329 +/- 0.073, n = 20 patients, P = .68). Prostaglandin endoperoxide H synthase-2 mRNA abundance was also unaffected by labor (CD: 0.933 +/- 0.255, n = 27 patients; SL: 0.714 +/- 0.179, n = 23 patients, mean +/- standard error, P = .66). Prostaglandin endoperoxide H synthase specific activity was positively and significantly (P < .05) correlated with both PGHS-1 and -2 mRNA levels. In situ hybridization showed the pervasive presence of both PGHS mRNAs in decidua cells with no detectable changes associated with labor.
Conclusion: Both isoforms of PGHS are present in term decidua and contribute to enzyme activity and prostaglandin production. Mechanisms regulating decidual prostanoid biosynthesis at labor do not involve changing the levels of expression of the two PGHS isoforms.