Rho/ROCK is Up‐regulated in Pulmonary Arteries of Pregnant Ewes in Chronic High Altitude Hypoxia

Abstract

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 to acute hypoxia (AJP, 2003). In this study, we examined the effect of chronic high altitude hypoxia (HAH) on cGMP-PKG-mediated relaxation. Isolated ovine intrapulmonary arteries (PAs) from pregnant ewes exposed to HAH (ewes kept at 12,470 ft altitude from ~35d to 145d gestation; term 150d) 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 analog of cGMP, or to DETA NONOate, a stable nitric oxide donor. We found that PAs relaxed to NO through both cGMP-dependent and independent mechanisms in normoxia. In chronic hypoxia, NO-mediated relaxation increased significantly, suggesting that guanylyl cyclase activity may be upregulated in these vessels. We observed minimal PKG-mediated relaxation both in normoxia or hypoxia. Furthermore, the inhibition of ROCK with a Rho-kinase-specific inhibitor (Y27632), induced increased relaxation of PAs to cGMP in chronic HAH PAs, but not in normoxic PAs, suggesting altered Rho/ROCK signaling under chronic HAH. We hypothesize that chronic high altitude hypoxia may induce sustained pulmonary vasoconstriction via increased protein expression and/or post-translational modification of ROCK or through altered protein-protein interactions involving Rho/ROCK, and that there is a compensatory upregulation of NO-cGMP mediated relaxation. HL059435, MIRS to S. Negash.