Proceedings of The Physiological Society

Kings College London (2005) J Physiol 565P, C175


Inhibition of the RhoA/Rho-kinase pathway attenuates hypoxia-induced angiogenesis in the pulmonary circulation

Hyvelin, Jean-Marc ; Howell, Katherine ; Preston, Robert J.; McLoughlin, Paul ;

1. Department of Physiology, Conway Institute of Biomolecular and Biomedical Research, Dublin, Ireland.

Chronic hypoxia leads to the development of pulmonary hypertension (PH) and right ventricular hypertrophy. The increase in pulmonary vascular resistance was previously attributed to encroachment of the remodelled arteriolar walls into the vascular lumen and loss of pulmonary blood vessels. We have recently demonstrated that chronic hypoxia leads to angiogenesis in the adult rat pulmonary circulation and increased area of the gas exchange membrane, a potentially beneficial adaptive response (Howell, K. et al.2003). Recent reports suggest that inhibition of the RhoA/Rho-kinase (ROK) pathway can prevent the development of hypoxic PH. However, blockade of this pathway has also been shown to prevent migration of endothelial cells in-vitro. Hence, we hypothesised that the ROK inhibitor Y27632 would inhibit the pulmonary angiogenesis induced by sustained hypoxia. Experiments were conducted on male Wistar Kyoto rats, anaesthetised (pentobarbital sodium 60mgkg-1) and killed by exsanguination. We assessed the pulmonary artery pressure (PAP) in isolated blood perfused lung from 3 different groups of rats: a control group, a chronically hypoxic (1week, FiO20.1, CH) group and a CH group orally treated with Y27632 (30mgkg-1day-1,CH-Y27632). In the CH group the mean (±SEM) PAP (13.7±0.4 mmHg, n=7) was significantly higher than that in the other groups (ANOVA, P<0.001), whereas the PAP was similar in both CH-Y27632 (9.5±0.4, n=7) and control groups (9.3±0.2 mmHg, n=7). Acute inhibition of ROK nearly normalized the PAP in the CH group, but had no effect in control and CH-Y27632 group. The total intra-acinar vessel length was significantly increased in CH lungs (9236±630 cmLL-1, P<0.001) and CH-Y27632 (7864±508 cmLL-1, P<0.05) when compared to the controls (5327±392 cmLL-1). The vessel lumen diameter was similar in all groups, whereas the ratio of wall thickness to lumen diameter was significantly (P<0.05) increased in the CH group, indicating that the vessels had remodelled. The endothelial surface area, the capillary length and the capillary volume were significantly increased in the CH lungs when compared to the two others groups. These data suggest: 1) that in chronic hypoxic PH the increase in pulmonary vascular resistance is not due to structural encroachment of the arteriolar wall into the lumen but predominantly due to RhoA/ROK mediated vasoconstriction and 2) that the RhoA/ROK pathway plays a key role in hypoxia-induced pulmonary angiogenesis.

Where applicable, experiments conform with Society ethical requirements