MECONIUM INHIBITS THE CONTRACTION OF UMBILICAL VESSELS INDUCED BY THETHROMBOXANE A(2) ANALOG U46619

OBJECTIVE: Our objective was to study the direct effects of meconium o n isolated umbilical artery and vein in vitro. STUDY DESIGN: Intact um bilical artery and vein rings were suspended in 5 ml organ baths conta ining Kreb's solution (pH 7.2, 37 degrees C; bubbled with 2.5% oxygen and 8.07% carbon dioxide, balance nitrogen) for isometric tension reco rding. Meconium alone (final bath concentration 1%), centrifuged and f iltered meconium, and meconium with the lipid fraction removed (separa ted into < 30,000 kd and > 30,000 kd) were added to the baths. Some ve ssels were also incubated in 1% meconium for 30 minutes, after which t he meconium was washed out. Concentration-response curves to U46619 we re obtained. The negative log of the concentration that evokes 50% of the maximal contraction was determined. RESULTS: Umbilical artery and vein had no sustained response to meconium. Tension that developed by rings exposed to meconium was significantly less than control at all c oncentrations of U46619. There was some loss of the efficacy of meconi um after centrifugation-filtration and washing out. Meconium without t he lipid fraction had less inhibitory effect than did native meconium. CONCLUSION: Meconium does not cause sustained contraction of umbilica l artery and vein in vitro. It does, however, inhibit the contractile effect of U46619 in both umbilical artery and vein smooth muscle. The inhibitory activity of meconium appears to be concentrated in the lipi d fraction.