Background We have shown that in pulmonary vessels, cGMP acts through cGMP-dependent protein kinase- (PKG) dependent and independent mechanisms to mediate vasodilation (JAP, 2000) and that cGMP-induced relaxation of pulmonary vessels is greater in normoxia compared with acute hypoxia (AJP, 2003).
Purpose In this study, we examined the effect of chronic high-altitude hypoxia (HAH) on cGMP-mediated relaxation.
Methods Isolated intrapulmonary veins (PVs), 2 to 3 mm in diameter, from pregnant ewes exposed to HAH (ewes kept at 12,470 ft altitude from ≈35 to 145 days' gestation; term 150 days) or matched normoxic controls were preconstricted with endothelin 1 and relaxed to 8-bromoguanosine 3′,5′-cyclic monophosphate (8-Br-cGMP), a cell membrane-permeable analogue of cGMP. Roles of PKG and Rho-kinase (ROCK) were assessed by determining cGMP-mediated relaxation in the presence of Rp-8-Br-cGMPS (PKG inhibitor) and Y27632 (Rho-kinase-specific inhibitor). ROCK protein expression and activity were measured.
Results We found that relaxation to cGMP was decreased in HAH PVs compared with controls. Inhibition of PKG did not affect cGMP-mediated relaxation in either control or HAH PVs. However, PKG protein expression was increased in HAH PVs compared with controls, indicating that PKG activity was inhibited in HAH vessels. Inhibition of ROCK with Y27632 restored relaxation to cGMP in HAH PVs to comparable levels as in control PVs, suggesting increased Rho/ROCK signaling in chronic HAH. Western blot analysis showed increased protein expression of ROCK-1 and ROCK-2 and increased expression of phosphorylated MYPT-1 serine 696 and threonine 853, indicating increased ROCK activity.
Conclusion Chronic HAH increases Rho/ROCK signaling in PVs of pregnant ewes, which decreases cGMP-mediated relaxation.
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