To determine whether angiogenesis is necessary for normal alveolarization, we studied the effects of two antiangiogenic agents, thalidomide and fumagillin, on alveolarization during a critical period of lung growth in infant rats. Newborn rats were treated with daily injections of fumagillin, thalidomide, or vehicle during the first 2 wk of life. Compared with control treatment, fumagillin and thalidomide treatment reduced lung weight-to-body weight ratio and pulmonary arterial density by 20 and 36%, respectively, and reduced alveolarization by 22%. Because these drugs potentially have nonspecific effects on lung growth, we also studied the effects of Su-5416, an inhibitor of the vascular endothelial growth factor receptor known as kinase insert domain-containing receptor/fetal liver kinase (KDR/flk)-1. As observed with the other antiangiogenic agents, Su-5416 treatment decreased alveolarization and arterial density. We conclude that treatment with three different antiangiogenic agents attenuated lung vascular growth and reduced alveolarization in the infant rat. We speculate that angiogenesis is necessary for alveolarization during normal lung development and that injury to the developing pulmonary circulation during a critical period of lung growth can contribute to lung hypoplasia.

RhoA GTPase mediates a variety of cellular responses, including activation of the contractile apparatus, growth, and gene expression. Acute hypoxia activates RhoA and, in turn, its downstream effector, Rho-kinase, and previous studies in rats have suggested a role for Rho/Rho-kinase signaling in both acute and chronically hypoxic pulmonary vasoconstriction. We therefore hypothesized that activation of Rho/Rho-kinase in the pulmonary circulation of mice contributes to acute hypoxic pulmonary vasoconstriction and chronic hypoxia-induced pulmonary hypertension and vascular remodeling. In isolated, salt solution-perfused mouse lungs, acute administration of the Rho-kinase inhibitor Y-27632 (1 x 10(-5) M) attenuated hypoxic vasoconstriction as well as that due to angiotensin II and KCl. Chronic treatment with Y-27632 (30 mg x kg(-1) x day(-1)) via subcutaneous osmotic pump decreased right ventricular systolic pressure, right ventricular hypertrophy, and neomuscularization of the distal pulmonary vasculature in mice exposed to hypobaric hypoxia for 14 days. Analysis of a small number of proximal pulmonary arteries suggested that Y-27632 treatment reduced the level of phospho-CPI-17, a Rho-kinase target, in hypoxic lungs. We also found that endothelial nitric oxide synthase protein in hypoxic lungs was augmented by Y-27632, suggesting that enhanced nitric oxide production might have played a role in the Y-27632-induced attenuation of chronically hypoxic pulmonary hypertension. In conclusion, Rho/Rho-kinase activation is important in the effects of both acute and chronic hypoxia on the pulmonary circulation of mice, possibly by contributing to both vasoconstriction and vascular remodeling.

Rho kinase signaling mediates increased basal pulmonary vascular tone in chronically hypoxic rats. Am J Physiol Lung Cell Mol Physiol 287: L665-L672, 2004. First published September 5, 2003 10.1152/ ajplung.00050.2003.-Recent evidence suggests that Rho/Rho kinase signaling plays an important role in the sustained vasoconstriction induced by many agonists and is involved in the pathogenesis of systemic vascular diseases. However, little is known about its role in increased vascular tone in hypoxic pulmonary hypertension (PH). The purpose of this study was to examine whether Rho/Rho kinasemediated Ca 2ϩ sensitization contributed to sustained vasoconstriction and increased vasoreactivity in hypoxic PH in rats. Acute intravenous administration of Y-27632, a Rho kinase inhibitor, nearly normalized the high pulmonary arterial blood pressure and total pulmonary resistance in chronically hypoxic rats. In contrast to nifedipine, Y-27632 also markedly decreased elevated basal vascular tone in hypertensive blood-perfused lungs and isolated pulmonary arteries. Y-27632 and another Rho kinase inhibitor, HA-1077, completely reversed nitro-L-arginine-induced vasoconstriction in physiological salt solution-perfused hypertensive lungs, whereas inhibitors of myosin light chain kinase (ML-9), protein kinase C (GF-109203X), phosphatidylinositol 3-kinase (LY-294002), and tyrosine kinase (tyrphostin A23) caused only partial or no reversal of the vasoconstriction. Vasoconstrictor responses to KCl were augmented in hypertensive physiological salt solution-perfused lungs and pulmonary arteries, and the augmentation was eliminated by Y-27632. These results suggest that Rho/Rho kinase-mediated Ca 2ϩ sensitization plays a central role in mediating sustained vasoconstriction and increased vasoreactivity in hypoxic PH.hypoxic pulmonary hypertension; Y-27632; calcium sensitization; RhoA SUSTAINED ABNORMAL VASOCONSTRICTION is one of the major causes of many cardiovascular diseases, including pulmonary hypertension (PH). ]. This is referred to as Ca 2ϩ sensitization (9, 43). Recent evidence indicates that although Ca 2ϩ /calmodulindependent MLCK-mediated MLC phosphorylation is the key factor for triggering VSMC contraction, Ca 2ϩ sensitization is important for the sustained phase of contraction (9, 43).The small GTPase RhoA, a member of the Rho family of small GTP-binding proteins, and its downstream effector Rho kinase (Rho/Rho kinase signaling) play a major role in the regulation of MLCP activity and, thus, Ca 2ϩ sensitization (9, 30, 43). RhoA is activated by various vasoconstrictors, including thromboxane, endothelin-1 (ET-1), and serotonin, the receptors of which are coupled to G proteins. Thus Rho/Rho kinase-mediated Ca 2ϩ sensitization is thought to be a major component in the sustained vasoconstriction induced by G protein-coupled receptor agonists. Selective Rho kinase inhibitors, such as Y-27632 (45) and fasudil (HA-1077) (2, 41, 45), effectively reverse the sustained vasoconstriction induced by many agonists (3,25,34).The pathogenesi...

We have found in chronically hypoxic rats that acute intravenous administration of the Rho kinase inhibitor Y-27632 nearly normalizes the pulmonary hypertension (PH) but has no pulmonary vascular selectivity. In this study, we tested if oral or inhaled Y-27632 would be an effective and selective pulmonary vasodilator in hypoxic PH. Although acute oral Y-27632 caused a marked and sustained decrease in mean pulmonary arterial pressure (MPAP), it also decreased mean systemic arterial pressure (MSAP). In contrast, 5 minutes of inhaled Y-27632 decreased MPAP without reducing MSAP. The hypotensive effect of inhaled Y-27632 on hypoxic PH was greater than that of inhaled nitric oxide, and the effect lasted for at least 5 hours. Inhaled fasudil, another Rho kinase inhibitor, caused selective MPAP reductions in monocrotaline-induced PH and in spontaneous PH in fawn-hooded rats, as well as in chronically hypoxic rats. These results suggested that inhaled Y-27632 was more effective than inhaled nitric oxide as a selective pulmonary vasodilator in hypoxic PH, and that Rho kinase-mediated vasoconstriction was also involved in the other models of PH. Inhaled Rho kinase inhibitors might be useful for acute vasodilator testing in patients with PH, and future work should evaluate their efficacy in the long-term treatment of PH.

No abstract