DEVELOPMENTAL DIFFERENCES IN ENDOTHELIUM-DEPENDENT RESPONSES IN ISOLATED OVINE PULMONARY-ARTERIES AND VEINS

Despite evidence for an important role for endothelium-derived relaxin g factor (EDRF) in transitional circulation, previous in vitro studies of newborn pulmonary arteries have demonstrated diminished EDRF activ ity when compared with arteries from older animals. We studied pulmona ry arteries and veins isolated from early newborn and juvenile sheep u sing standard tissue bath techniques. Incubation of vessels with the n itric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NNA) const ricted veins but not arteries from both age groups. Further studies us ing preconstricted vessels revealed that arteries relaxed to acetylcho line (ACh), with significantly greater responses observed in juvenile arteries. Veins from both age groups contracted to ACh. Pretreatment w ith prostaglandin inhibitors (indomethacin and SQ 29,548) diminished A Ch relaxations in pulmonary arteries from both age groups, greatly enh anced relaxations to ACh in newborn pulmonary veins, and depressed con tractions in juvenile pulmonary veins. Removal of endothelium mechanic ally or functionally with prostaglandin inhibitors and L-NNA eliminate d relaxations to ACh in pulmonary arteries from both age groups and re sulted in contractions in veins. We conclude that isolated pulmonary v eins from newborn sheep exhibit both baseline and stimulated release o f EDRF, and we speculate that these venous responses may be important in the transitional pulmonary circulation.