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Chronic pulmonary hypertension in infancy and childhood is characterized by a fixed and progressive increase in pulmonary arterial pressure and resistance, pulmonary arterial remodeling, and right ventricular hypertrophy and systolic dysfunction. These abnormalities are replicated in neonatal rats chronically exposed to hypoxia from birth in which increased activity of Rho-kinase (ROCK) is critical to injury, as evidenced by preventive effects of ROCK inhibitors. Our objective in the present study was to examine the reversing effects of a late or rescue approach to treatment with a ROCK inhibitor on the pulmonary and cardiac manifestations of established chronic hypoxic pulmonary hypertension. Rat pups were exposed to air or hypoxia (13% [O.sub.2]) from postnatal day 1 and were treated with Y-27632 (15 mg/kg) or saline vehicle by twice daily subcutaneous injection commencing on day 14, for up to 7 days. Treatment with Y-27632 significantly attenuated right ventricular hypertrophy, reversed arterial wall remodeling, and completely normalized fight ventricular systolic function in hypoxia-exposed animals. Reversal of arterial wall remodeling was accompanied by increased apoptosis and attenuated content of endothelin (ET)-1 and [ET.sub.A] receptors. Treatment of primary cultured juvenile rat pulmonary artery smooth muscle cells with Y-27632 attenuated serum-stimulated ROCK activity and proliferation and increased apoptosis. Smooth muscle apoptosis was also induced by short interfering RNA-mediated knockdown of ROCK-II, but not of ROCK-I. We conclude that sustained rescue treatment with a ROCK inhibitor reversed both the hemodynamic and structural abnormalities of chronic hypoxic pulmonary hypertension in juvenile rats and normalized right ventricular systolic function. Attenuated expression and activity of ET-1 and its A-type receptor on pulmonary arterial smooth muscle was a likely contributor to the stimulatory effects of ROCK inhibition on apoptosis. In addition, our data suggest that ROCK-II may be dominant in enhancing survival of pulmonary arterial smooth muscle. hypoxia; endothelin-1; apoptosis; smooth muscle cells doi: 10.1152/ajpheart.00595.2010.

Hypercapnia is regularly observed in chronic lung disease, such as bronchopulmonary dysplasia in preterm infants. Hypercapnia results in increased nitric oxide synthase activity and in vitro formation of nitrates. Neural vasculature of the immature subject is particularly sensitive to nitrative stress. We investigated whether exposure to clinically relevant sustained high C[O.sub.2] causes microvascular degeneration in the newborn brain by inducing nitrative stress, and whether this microvascular degeneration has an impact on brain growth. Newborn rat pups were exposed to 10% C[O.sub.2] as inspired gas ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] = 60-70 mmHg) starting within 24 h of birth until postnatal day 7 (P7). Brains were notably collected at different time points to measure vascular density, determine brain cortical nitrite/nitrate, and trans-arachidonic acids (TAAs; products of nitration) levels as effectors of vessel damage. Chronic exposure of rat pups to high C[O.sub.2] [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] [approximately equal to] 65 mmHg) induced a 20% loss in cerebrovascular density at P3 and a 15% decrease in brain mass at P7; at P30, brain mass remained lower in C[O.sub.2]-exposed animals. Within 24 h of exposure to C[O.sub.2], brain eNOS expression and production of nitrite/nitrate doubled, lipid nitration products (TAAs) increased, and protein nitration (3-nitrotyrosine immunoreactivity) was also coincidently augmented on brain microvessels (lectin positive). Intracerebroventricular injection of TAAs (10 [micro]M) replicated cerebrovascular degeneration. Treatment of rat pups with NOS inhibitor (L-[N.sup.[omega]]-nitroarginine methyl ester) or a peroxynitrite decomposition catalyst (FeTPPS) prevented hypercapnia-induced microvascular degeneration and preserved brain mass. Cytotoxic effects of high C[O.sub.2] were reproduced in vitro/ex vivo on cultured endothelial cells and sprouting microvessels. In summary, hypercapnia at values frequently observed in preterm infants with chronic lung disease results in increased nitrative stress, which leads to cerebral cortical microvascular degeneration and curtails brain growth. brain microvasculature; cell death; reactive nitrogen species; transfatty acids. doi: 10.1152/ajpregu.00807.2009.

Permissive hypercapnia, achieved using low tidal volume ventilation, has been an effective protective strategy in patients with acute respiratory distress syndrome. To date, no such protective effect has been demonstrated for the chronic neonatal lung injury, bronchopulmonary dysplasia. The objective of our study was to determine whether evolving chronic neonatal lung injury, using a rat model, is resistant to the beneficial effects of hypercapnia or simply requires a less conservative approach to hypercapnia than that applied clinically to date. Neonatal rats inhaled air or 60% [O.sub.2] for 14 days with or without 5.5% C[O.sub.2]. Lung parenchymal neutrophil and macrophage numbers were significantly increased by hyperoxia alone, which was associated with interstitial thickening and reduced secondary crest formation. The phagocyte influx, interstitial thickening, and impaired alveolar formation were significantly attenuated by concurrent hypercapnia. Hyperoxic pups that received 5.5% C[O.sub.2] had a significant increase in alveolar number relative to air-exposed pups. Increased tyrosine nitration, a footprint for peroxynitrite-mediated reactions, arteriolar medial wall thickening, and both reduced small peripheral pulmonary vessel number and VEGF and angiopoietin-1 (Ang-1) expression, which were observed with hyperoxia, was attenuated by concurrent hypercapnia. We conclude that evolving chronic neonatal lung injury in a rat model is responsive to the beneficial effects of hypercapnia. Inhaled 5.5% C[O.sub.2] provided a significant degree of protection against parenchymal and vascular injury in an animal model of chronic neonatal lung injury likely due, at least in part, to its inhibition of a phagocyte influx. carbon dioxide; lung growth; inflammation doi: 10.1152/ajplung.00139.2009.

In rats, chronic hypercapnia has been reported to ameliorate hypoxia-induced pulmonary hypertension in newborn and adult and to enhance endothelium-dependent vasorelaxation in adult pulmonary arteries. The underlying mechanisms accounting for chronic hypercapnia-induced improvements in pulmonary vascular function are not understood. Hypothesizing that downregulation of arginase activity may be contributory, we examined relaxation responses and arginase activity and expression in pulmonary arteries from newborn rats that were exposed (from birth to 14 days) to either mild-to-moderate (5.5% inhaled C[O.sub.2]) or severe (10% COz) hypercapnia with either normoxia or hypoxia (13% [O.sub.2]). Pulmonary arteries from pups exposed to normoxia and chronic hypercapnia (5.5 or 10% C[O.sub.2]) contracted less in response to a thromboxane [A.sub.2] analog, U-46619, and showed enhanced endothelium-dependent (but not independent) relaxation compared with arteries from normocapnic pups (P < 0.01). Parallel with these changes, arginase activity and arginase I (but not II) expression in lung and pulmonary arterial tissue were significantly decreased (P < 0.05). Exposure to 10% C[O.sub.2] significantly increased (P < 0.01) pulmonary arterial tissue nitric oxide (nitrite) generation. In pups chronically exposed to hypoxia (13% [O.sub.2]), severe hypercapnia (10% C[O.sub.2]) significantly (P < 0.05) enhanced endothelium-dependent relaxation, increased nitric oxide generation, and decreased arginase activity but not expression. We conclude that chronic hypercapnia-induced down-regulation of lung arginase expression and/or activity may reduce pulmonary vascular resistance by enhancing nitric oxide generation and thus endothelium-dependent relaxation. This mechanism may explain some of the beneficial effects of chronic hypercapnia on experimental pulmonary hypertension. pulmonary vascular resistance; nitric oxide; hypoxia doi: 10.1152/ajplung.00047.2009

Xanthine oxidase (XO)-derived reactive oxygen species (ROS) formation contributes to experimental chronic hypoxic pulmonary hypertension in adults, but its role in neonatal pulmonary hypertension has received little attention. In rats chronically exposed to hypoxia (13% [O.sub.2]) for 14 days from birth, we examined the effects of ROS scavengers (U74389G 10 mg*[kg.sup.-1]*[day.sup.-1] or Tempol 100 mg*[kg.sup.-1]*[day.sup.-1] ip) or a XO inhibitor, Allopurinol (50 mg*[kg .sup.-1]*[day.sup.-1] ip). Both ROS scavengers limited oxidative stress in the lung and attenuated hypoxia-induced vascular remodeling, confirming a critical role for ROS in this model. However, both interventions also significantly inhibited somatic growth and normal cellular proliferation in distal air spaces. Hypoxiaexposed pups had evidence of increased serum and lung XO activity, increased vascular XO-derived superoxide production, and vascular nitrotyrosine formation. These changes were all prevented by treatment with Allopurinol, which also attenuated hypoxia-induced vascular remodeling and partially reversed inhibited endothelium-dependent arterial relaxation, without affecting normal growth and proliferation. Collectively, our findings suggest that XO-derived superoxide induces endothelial dysfunction, thus impairing pulmonary arterial relaxation, and contributes to vascular remodeling in hypoxia-exposed neonatal rats. Due to the potential for adverse effects on normal growth, targeting XO may represent a superior 'antioxidant' strategy to ROS scavengers for neonates with pulmonary hypertension. antioxidants; allopurinol; U74389G; Tempol; 8-isoprostane

Pulmonary hypertension (PHT) in neonates is often refractory to the current best therapy, inhaled nitric oxide (NO). The utility of a new class of pulmonary vasodilators, Rho-kinase (ROCK) inhibitors, has not been examined in neonatal animals. Our objective was to examine the activity and expression of RhoA/ROCK in normal and injured pulmonary arteries and to determine the short-term pulmonary hemodynamic (assessed by pulse wave Doppler) effects of ROCK inhibitors (15 mg/kg ip Y-27632 or 30 mg/kg ip fasudil) in two neonatal rat models of chronic PHT with pulmonary vascular remodeling (chronic hypoxia, 0.13 [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] or 1 mg [.kg .sup.-1] [day.sup.-1] ip chronic bleomycin for 14 days from birth). Activity of the RhoA/ROCK pathway and ROCK expression were increased in hypoxia- and bleomycin-induced PHT. In both models, severe PHT [characterized by raised pulmonary vascular resistance (PVR) and impaired right ventricular (RV) performance] did not respond acutely to inhaled NO (20 ppm for 15 min) or to a single bolus of a NO donor, 3-morpholinosydnonimine hydrochloride (SIN- 1; 2 [micro]g/kg ip). In contrast, a single intraperitoneal bolus of either ROCK inhibitor (Y-27632 or fasudil) completely normalized PVR but had no acute effect on RV performance. ROCK-mediated vasoconstriction appears to play a key role in chronic PHT in our two neonatal rat models. Inhibitors of ROCK have potential as a testable therapy in neonates with PHT that is refractory to NO. Y-27632; fasudil; two-dimensional echocardiography; pulse wave Doppler; SIN-1

Induction of hypercapnia by breathing high concentrations of carbon dioxide (C[O.sub.2]) may have beneficial effects on the pulmonary circulation. We tested the hypothesis that exposure to C[O.sub.2] would protect against chronic pulmonary hypertension in newborn rats. Atmospheric C[O.sub.2] was maintained at carbon dioxide; endothefin; oxidant stress; 8-isoprostane; echocardiography

Newborn rats exposed to 60% [O.sub.2] for 14 days develop endothelin (ET)-1-dependent pulmonary hypertension with vascular remodeling, characterized by increased smooth muscle cell (SMC) proliferation and medial thickening of pulmonary resistance arteries. Using immunohistochemistry and Western blot analyses, we examined the effect of exposure to 60% [O.sub.2] on expression in the lung of receptors for the platelet-derived growth factors (PDGF), which are implicated in the pathogenesis of arterial smooth muscle hyperplasia. We observed a marked [O.sub.2]-induced upregulation of PDGF-[alpha] and -[beta] receptors (PDGF-[alpha]R and -[beta]R) on arterial smooth muscle. This led us to examine pulmonary vascular PDGF receptor expression in 60% [O.sub.2]-exposed rats given SB-217242, a combined ET receptor antagonist, which we found prevented the [O.sub.2]-induced upregulation of PDGF-[beta]R, but not PDGF[alpha]R, on arterial smooth muscle. PDGF-BB, a major PDGF-[beta]R ligand, was found to be a potent in vitro inducer of hyperplasia and DNA synthesis in cultured pulmonary artery SMC from infant rats. A critical role for PDGF-[beta]R ligands in arterial SMC proliferation was confirmed in vivo using a truncated soluble PDGF-[beta]R intervention, which attenuated SMC proliferation induced by exposure to 60% [O.sub.2] Collectively, these data are consistent with a major role for PDGF-[beta]R-mediated SMC proliferation, acting downstream of increased ET-1 in a newborn rat model of 60% [O.sub.2]-induced pulmonary hypertension. pulmonary oxygen toxicity; vascular smooth muscle; growth factors; soluble receptors

The article discusses a study on chronic neonatal pulmonary hypertension (PH) using a monocrotaline (MCT) rat model. Topics include developmental lung disorders associated with PH, some of the factors contributing to PH in the neonatal period such as altered vasoreactivity, perinatal infection and inflammation, and the effects of the MCT toxin used in the study to investigate adult PH. Also included are the features reminiscent of neonatal PH induced by MCT when administered to infant rats.

Purpose: To investigate the dependence of dissolved 129Xe chemical shift on the fraction of inhaled oxygen, FiO2, in the lungs of healthy rats. Methods: The chemical shifts of 129Xe dissolved in red blood cells, δRBC, and blood plasma and/or tissue, δPlasma, were measured using MRS in 12 Sprague Dawley rats mechanically ventilated at FiO2 values of 0.14, 0.19, and 0.22. Regional effects on the chemical shifts were controlled using a chemical shift saturation recovery sequence with a fixed delay time. MRS was also performed at an FiCO2 value of 0.085 to investigate the potential effect of the vascular response on δRBC and δPlasma. Results: δRBC increased with decreasing FiO2 (P =.0002), and δPlasma showed no dependence on FiO2 (P =.23). δRBC at FiCO2 = 0 (210.7 ppm ± 0.1) and at FiCO2 = 0.085 (210.6 ppm ± 0.2) were not significantly different (P =.67). δPlasma at FiCO2 = 0 (196.9 ppm ± 0.3) and at FiCO2 = 0.085 (197.0 ppm ± 0.1) were also not significantly different (P =.81). Conclusion: Rat lung δRBC showed an inverse relationship to FiO2, opposite to the relationship previously demonstrated for in vitro human blood. Rat lung δRBC did not depend on FiCO2. [ABSTRACT FROM AUTHOR]