COORDINATE EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE AND CYCLOOXYGENASE-2 GENES IN UTERINE TISSUES OF ENDOTOXIN-TREATED PREGNANT MICE

OBJECTIVES: Our purpose was to investigate the relationship between ex pression of cyclooxygenase-2 and inducible nitric oxide synthase genes after labor induction with bacterial lipopolysaccharide in a murine m odel of preterm parturition. STUDY DESIGN: Pregnant C57BI/6 mice were given Escherichia coli lipopolysaccharide (20 mu g per mouse) by intra peritoneal injection on day 16 of gestation, and the animals were foll owed up for signs of labor. Control mice received an equivalent volume of 0.9% saline solution. The latency from lipopolysaccharide injectio ns until appearance of the first pup was recorded. Two separate groups of mice were given either aminoguanidine or indomethacin (5 mg/kg int ragastric) 24 hours before induction of preterm labor. In a separate s et of experiments mice were treated with lipopolysaccharide as describ ed and were killed at intervals from 0.5 to 72 hours and intrauterine tissues (uterus, placenta, and fetal membranes) were removed and snap frozen in liquid nitrogen. Total protein and ribonucleic acid were ext racted for Western and Northern blot analysis of cyclooxygenase-2 and inducible nitric oxide synthase protein and messenger ribonucleic acid , respectively. RESULTS: Northern blots from uterine, placental, and f etal membrane tissues of lipopolysaccharide-and saline solution-treate d mice revealed that cyclooxygenase-2 and inducible nitric oxide synth ase messenger ribonucleic acid transcripts were rapidly (within 0.5 to 2 hours) up-regulated after lipopolysaccharide administration but wer e unchanged in mice injected with saline solution. Immunoblot analysis with isoform-specific antibodies revealed that both enzymes were expr essed in uterus, placenta, and fetal membranes in a coordinated fashio n with peak expression seen at 6 to 8 hours. Although the steady-state accumulation of messenger ribonucleic acid transcripts encoding cyclo oxygenase-2 and inducible nitric oxide synthase peaked at 6 hours and declined to baseline by 16 hours after injection with lipopolysacchari de, expression of cyclooxygenase-2 and inducible nitric oxide synthase was sustained through the period when premature delivery was observed . Nitric oxide-dependent cyclooxygenase-2 and inducible nitric oxide s ynthase expression was demonstrated by the elimination of accumulation of both messenger ribonucleic acid transcripts in mice pretreated wit h aminoguanidine before injection with lipopolysaccharide. CONCLUSIONS : These data indicate that nitric oxide synthesis may be a prerequisit e for subsequent stimulation of cyclooxygenase-2 and inducible nitric oxide synthase gene expression. Taken together, the data suggest that cyclooxygenase-2 and inducible nitric oxide synthase are expressed in a coordinated manner in the uterus of endotoxin-challenged pregnant mi ce and that their enzymatic products may contribute to the signaling o f uterine activity or cervical changes culminating in expulsion of the fetus.