Rh. Steinhorn et al., DEVELOPMENTAL DIFFERENCES IN ENDOTHELIUM-DEPENDENT RESPONSES IN ISOLATED OVINE PULMONARY-ARTERIES AND VEINS, The American journal of physiology, 264(6), 1993, pp. 2162-2167
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.