Imaging of the pulmonary circulation in the closed-chest rat using synchrotron radiation microangiography.

Structural changes of the pulmonary circulation during the pathogenesis of pulmonary arterial hypertension remain to be fully elucidated. Although angiography has been used for visualizing the pulmonary circulation, conventional angiography systems have considerable limitations for visualizing small microvessels (diameters < 200 microm), particularly within a closed-chest animal model. In this study we assess the effectiveness of monochromatic synchrotron radiation (SR) for microangiography of the pulmonary circulation in the intact-chest rat. Male adult Sprague-Dawley rats were anesthetized, and a catheter was positioned within the right ventricle, for administering iodinated contrast agent (Iomeron 350). Subsequently, microangiography of pulmonary arterial branches within the left lung was performed using monochromatic SR. Additionally, we assessed dynamic changes in vessel diameter during acute hypoxic (10% and 8% O2 for 4 min each) pulmonary vasoconstriction (HPV). Using SR we were able to visualize pulmonary microvessels with a diameter of <100 microm (the 4th generation of branching from the left axial artery). Acute hypoxia caused a significant decrease in the diameter of all vessels less than 500 microm. The greatest degree of pulmonary vasoconstriction was observed in vessels with a diameter between 200 and 300 microm. These results demonstrate the effectiveness of SR for visualizing pulmonary vessels in a closed-chest rat model and for assessing dynamic changes associated with HPV. More importantly, these observations implicate SR as an effective tool in future research for assessing gross structural changes associated with the pathogenesis of pulmonary arterial hypertension.     

Changes in macrovessel pulmonary blood flow distribution following chronic hypoxia: assessed using synchrotron radiation microangiography.

Structural and functional changes of the pulmonary circulation, particularly during the pathogenesis of pulmonary arterial hypertension (PAH), remain to be fully elucidated. In this study, we utilized monochromatic synchrotron radiation (SR) microangiography to assess changes in pulmonary arteriole blood flow in the intact-chest rat after 4 wk of chronic hypoxia. Sprague-Dawley rats were exposed to normoxia (N-rats) or chronic hypoxia (10% O(2); CH-rats) for 28 days. Rats were anesthetized, and microangiography was performed on the left lung to assess 1) the branching distribution of pulmonary arteriole blood flow (internal diameter >80 microm) and 2) dynamic changes in vessel lumen diameter during acute hypoxic (8% O(2) for 4 min) pulmonary vasoconstriction (HPV) before and after beta-adrenoceptor blockade (2 mg/kg i.v. propranolol). Using SR angiography, we observed that the number of opaque third- and fourth-generation vessels (100-300 microm) for CH-rats was significantly fewer than the number for N-rats. The magnitude of HPV was not different between CH-rats and N-rats. Beta-adrenoceptor blockade accentuated the HPV in 200- to 300-microm vessels for CH-rats, but even more so in N-rats. However, in CH-rats, beta-adrenoceptor blockade also accentuated the HPV in 100- to 200-microm vessels. In summary, we utilized SR to assess gross blood flow changes and functional changes (i.e., HPV) of the pulmonary circulation in PAH. These results highlight the benefits of SR for assessing pulmonary circulatory pathology. Of particular importance, future use of SR will provide an effective method for assessing potential therapeutic treatments for PAH.     

Role of endogenous nitric oxide generation in the regulation of vascular tone and reactivity in small vessels as investigated in transgenic mice using synchrotron radiation microangiography.

Nitric oxide (NO) produced by endothelial NO synthase (eNOS) plays a central role in regulation of vascular tone and reactivity. The purpose of this study is to clarify the basal tone and microvascular reactivity in eNOS-overexpressing transgenic (Tg) mice in vivo with a microangiography system using monochromatic synchrotron radiation (SR). The mouse femoral artery was cannulated, nonionic contrast media was injected, and microangiography was performed in hindlimbs of mice. Serial images of the small blood vessels (diameter <200 microm) were recorded by the SR microangiography system. At basal conditions, the diameter of tibial arteries in eNOS-Tg mice was larger than that of wild-type mice (179 +/- 8 versus 132 +/- 8 microm; P < 0.01). l-NAME treatment decreased the vessel diameter and canceled the difference in vessel diameters between two genotypes. Acetylcholine- and sodium nitroprusside-induced relaxations of small vessels were significantly reduced in Tg mice compared with wild-type mice (35.0 +/- 9.4 versus 61.6 +/- 6.7%, 85.0 +/- 10.2 versus 97.3 +/- 6.7% of the maximum relaxation, respectively). Our data provide the evidence that overproduced NO from endothelium reduces vascular tone and plays a pivotal role in regulation of vascular tone in small vessels. Furthermore, the reduced NO-mediated relaxation in small vessels of eNOS-Tg mice is demonstrated for the first time in vivo. SR microangiography allows us to evaluate the reactivity in small-sized vessels and appears to be a powerful tool for assessing the microvascular circulation in vivo.     

Role of Rho-kinase signaling and endothelial dysfunction in modulating blood flow distribution in pulmonary hypertension

Rho-kinase-mediated vasoconstriction and endothelial dysfunction are considered two primary instigators of pulmonary arterial hypertension (PAH). However, their contribution to the adverse changes in pulmonary blood flow distribution associated with PAH has not been addressed. This study utilizes synchrotron radiation microangiography to assess the specific role, and contribution of, Rho-kinase-mediated vasoconstriction and endothelial dysfunction in PAH. Male adult Sprague-Dawley rats were injected with saline (Cont-rats) or monocrotaline (MCT-rats) 3 wk before microangiography was performed on the left lung. We assessed dynamic changes in vessel internal diameter (ID) in response to 1) the Rho-kinase inhibitor fasudil (10 mg/kg iv); or 2) ACh (3 μg · kg?1 · min?1), sodium nitroprusside (SNP, 5 μg · kg?1 · min?1), and N(ω)-nitro-l-arginine methyl ester (l-NAME, 50 mg/kg iv). We observed that MCT-rats had fewer vessels of the microcirculation compared with Cont-rats. The fundamental result of this study is that fasudil improved pulmonary blood flow distribution and reduced pulmonary pressure in PAH rats, not only by dilating already-perfused vessels (ID > 100 μm), but also by restoring blood flow to vessels that had previously been constricted closed (ID < 100 μm). Endothelium-dependent vasodilation was impaired in MCT-rats primarily in vessels with an ID < 200 μm. Moreover the vasoconstrictor response to l-NAME was accentuated in MCT-rats, but only in the 200- to 300-μm vessels. These results highlight the importance of Rho-kinase-mediated control and endothelial control of pulmonary vascular tone in PAH. Indeed, an effective therapeutic strategy for treating PAH should target both the smooth muscle Rho-kinase and endothelial pathways.     

Phosphodiesterase 5 inhibition restores impaired ACh relaxation in hypertensive conduit pulmonary arteries

Responses to acetylcholine (ACh) and sodium nitroprusside (SNP) were compared in large (LPA) and small pulmonary artery (SPA) rings from normoxic and chronically hypoxic (CH) rats. In addition, the effects of a selective phosphodiesterase (PDE) 5 inhibitor, E-4021, on ACh-induced relaxation were evaluated. Chronic hypoxia markedly decreased both ACh- and SNP-induced relaxations in LPA but not in SPA rings. Pretreatment with E-4021 caused a much greater leftward shift of the concentration-response curve for ACh in hypoxic than in normoxic LPA rings, eliminating the difference in response to ACh between these two vessels. These results suggest that cGMP-dependent relaxation is impaired in the proximal but not in the distal pulmonary artery of CH rats and that increased PDE5 activity could be a mechanism responsible for this impaired responsiveness.     

Stochastic Simulation of Human Pulmonary Blood Flow and Transit Time Frequency Distribution Based on Anatomic and Elasticity Data

The objective of our study was to develop a computing program for computing the transit time frequency distributions of red blood cell in human pulmonary circulation, based on our anatomic and elasticity data of blood vessels in human lung. A stochastic simulation model was introduced to simulate blood flow in human pulmonary circulation. In the stochastic simulation model, the connectivity data of pulmonary blood vessels in human lung was converted into a probability matrix. Based on this model, the transit time of red blood cell in human pulmonary circulation and the output blood pressure were studied. Additionally, the stochastic simulation model can be used to predict the changes of blood flow in human pulmonary circulation with the advantage of the lower computing cost and the higher flexibility. In conclusion, a stochastic simulation approach was introduced to simulate the blood flow in the hierarchical structure of a pulmonary circulation system, and to calculate the transit time distributions and the blood pressure outputs.     

Cyclooxygenase contracting factors and altered pulmonary vascular responses in chronically hypoxic newborn pigs.

Pulmonary hypertension and blunted pulmonary vascular responses to ACh develop when newborn pigs are exposed to chronic hypoxia for 3 days. To determine whether a cyclooxygenase (COX)-dependent contracting factor, such as thromboxane, is involved with altered pulmonary vascular responses to ACh, newborn piglets were raised in 11% O(2) (hypoxic) or room air (control) for 3 days. Small pulmonary arteries (100-400 microm diameter) were cannulated and pressurized, and their responses to ACh were measured before and after either the COX inhibitor indomethacin; a thromboxane synthesis inhibitor, dazoxiben or feregrelate; or the thromboxane-PGH(2)-receptor antagonist SQ-29548. In control arteries, indomethacin reversed ACh responses from dilation to constriction. In contrast, hypoxic arteries constricted to ACh before indomethacin and dilated to ACh after indomethacin. Furthermore, ACh constriction in hypoxic arteries was nearly abolished by either dazoxiben, feregrelate, or SQ-29548. These findings suggest that thromboxane is the COX-dependent contracting factor that underlies the constrictor response to ACh that develops in small pulmonary arteries of piglets exposed to 3 days of hypoxia. The early development of thromboxane-mediated constriction may contribute to the pathogenesis of chronic hypoxia-induced pulmonary hypertension in newborns.     

Morphometry of cat's pulmonary arterial tree

Morphometic data of the pulmonary artery in the cat's right lung are presented. Silicone elastomer casts of cat's right lung were made, and measured, counted and analyzed. The Strahler system is used to describe the branching pattern of the arterial vascular tree. These data are needed for any quantitative approach to the study of the pulmonary circulation. For all the pulmonary blood vessels of the cat lying between the main pulmonary artery and the capillary beds, there are a total of 10 orders of vessels in the right upper lobe, 9 orders of vessels in the right middle lobe and 11 orders of vessels in the right lower lobe. The ratio of the number of branches in successive orders of vessels or the branching ratio, is 3.58. The corresponding average diameter ratio is 1.72, whereas the average length ratio is 1.81.     

Application of Thinned-Skull Cranial Window to Mouse Cerebral Blood Flow Imaging Using Optical Microangiography

In vivo imaging of mouse brain vasculature typically requires applying skull window opening techniques: open-skull cranial window or thinned-skull cranial window. We report non-invasive 3D in vivo cerebral blood flow imaging of C57/BL mouse by the use of ultra-high sensitive optical microangiography (UHS-OMAG) and Doppler optical microangiography (DOMAG) techniques to evaluate two cranial window types based on their procedures and ability to visualize surface pial vessel dynamics. Application of the thinned-skull technique is found to be effective in achieving high quality images for pial vessels for short-term imaging, and has advantages over the open-skull technique in available imaging area, surgical efficiency, and cerebral environment preservation. In summary, thinned-skull cranial window serves as a promising tool in studying hemodynamics in pial microvasculature using OMAG or other OCT blood flow imaging modalities.     

Plexiform-like lesions and increased tissue factor expression in a rat model of severe pulmonary arterial hypertension

Severe pulmonary arterial hypertension (PAH) occurs in idiopathic form and in association with diverse diseases. The pathological hallmarks are distal smooth muscle hypertrophy, obliteration of small pulmonary arteriole lumens, and disorganized cellular proliferation in plexiform lesions. In situ thrombosis is also observed. A detailed understanding of the disease progression has been hampered by the absence of an animal model bearing all the pathological features of human disease. To create a model with these characteristics, we gave young (200-g) rats monocrotaline 1 wk following left pneumonectomy; controls with vehicle treatment or sham operation were also studied. In experimental rats, pulmonary arteries had distal smooth muscle hypertrophy and proliferative perivascular lesions. The lesions had a plexiform appearance, occurred early in disease development, and were composed of cells expressing endothelial antigens. Three-dimensional microangiography revealed severe vascular pruning and disorganized vascular networks. We found that expression of tissue factor (TF), the membrane glycoprotein that initiates coagulation, facilitates angiogenesis, and mediates arterial injury in the systemic circulation, was increased in the pulmonary arterioles and plexiform-like lesions of the rats. TF was also heavily expressed in the vessels and plexiform lesions of humans with pulmonary arterial hypertension. We conclude that plexiform-like lesions can be reproduced in rats, and this model will facilitate experiments to address controversies about the role of these lesions in PAH. Increased TF expression may contribute to the prothrombotic diathesis and vascular cell proliferation typical of human disease.     

The combined use of 131I-labeled antibody and the hypoxic cytotoxin SR 4233 in vitro and in vivo.

Radioimmunotherapy is hindered by the slow penetration of antibody molecules into tumors. Cells that are poorly targeted by antibody, because of their distance from feeding blood vessels, receive the lowest radiation dose, and this problem is compounded if there are radioresistant hypoxic cells present. It would be desirable to combine radioimmunotherapy with an agent that is preferentially toxic to these cells. SR 4233 is a potent hypoxic cytotoxin, and it was combined with 131I-NR-LU-10 to treat LS174T human colon adenocarcinoma multicell spheroids and nude mouse xenografts for these studies. Under conditions of severe hypoxia (< 0.01% O2), 2 h of pretreatment or 18 h of simultaneous treatment with SR 4233 did not significantly enhance the effectiveness of 131I-NR-LU-10 in spheroids. However, under aerobic conditions with a 10% fraction of hypoxic cells, there was more toxicity than would be predicted from simple additivity. Xenografts treated with 131I-NR-LU-10 + SR 4233 had a growth delay that was significantly longer than that achieved with 131I-NR-LU-10 alone. In both spheroids and xenografts, combined treatment produced about 10 times more cell killing than 131I-NR-LU-10 alone. The lack of enhancement in spheroids under complete hypoxia suggests that SR 4233 does not sensitize hypoxic cells to radiation damage. The results with aerobic spheroids and in vivo, where a portion of the cells were hypoxic, could be explained by the targeting of different cell populations (hypoxic and aerobic) by each therapeutic modality. This effect should also be enhanced by reoxygenation and reestablishment of the hypoxic fraction during treatment, thus allowing more than the initially hypoxic fraction of cells to be killed by the SR 4233.     

Mice expressing BMPR2R899X transgene in smooth muscle develop pulmonary vascular lesions

Familial pulmonary arterial hypertension (PAH) is associated with mutations in bone morphogenetic protein type II receptor (BMPR2). Many of these mutations occur in the BMPR2 tail domain, leaving the SMAD functions intact. To determine the in vivo consequences of BMPR2 tail domain mutation, we created a smooth muscle-specific doxycycline-inducible BMPR2 mutation with an arginine to termination mutation at amino acid 899. When these SM22-rtTA x TetO(7)-BMPR2(R899X) mice had transgene induced for 9 wk, starting at 4 wk of age, they universally developed pulmonary vascular pruning as assessed by fluorescent microangiography. Approximately one-third of the time, the induced animals developed elevated right ventricular systolic pressures (RVSP), associated with extensive pruning, muscularization of small pulmonary vessels, and development of large structural pulmonary vascular changes. These lesions included large numbers of macrophages and T cells in their adventitial compartment as well as CD133-positive cells in the lumen. Small vessels filled with CD45-positive and sometimes CD3-positive cells were a common feature in all SM22-rtTA x TetO(7)-BMPR2(R899X) mice. Gene array experiments show changes in stress response, muscle organization and function, proliferation, and apoptosis and developmental pathways before RVSP increases. Our results show that the primary phenotypic result of BMPR2 tail domain mutation in smooth muscle is pulmonary vascular pruning leading to elevated RVSP, associated with early dysregulation in multiple pathways with clear relevance to PAH. This model should be useful to the research community in examining early molecular and physical events in the development of PAH and as a platform to validate potential treatments.     

Lysophosphatidic acid enhances airway response to acetylcholine in guinea pigs.

Inhalation of lysophosphatidic acid (LPA, 1-100 microg/ml) for 2 min enhanced the airway response induced by intravenous injection of ACh in guinea pigs. At 30 min after inhalation of LPA, the airway response to ACh was two fold higher than that before inhalation. This enhancement of airway response to ACh was partially inhibited by capsaicin desensitization or bilateral vagotomy. These results suggested that the enhancement of airway response to ACh induced by LPA may be due to the activation of capsaicin-sensitive fibers. It can be also contribute to bronchial asthma or other types of pulmonary disease such as cough variant asthma and atopic cough.     

Cyclooxygenase-2 and an early stage of chronic hypoxia-induced pulmonary hypertension in newborn pigs.

Our objective was to determine whether cyclooxygenase (COX)-2-dependent metabolites contribute to the altered pulmonary vascular responses that manifest in piglets with chronic hypoxia-induced pulmonary hypertension. Piglets were raised in either room air (control) or hypoxia for 3 days. The effect of the COX-2 selective inhibitor NS-398 on responses to arachidonic acid or acetylcholine (ACh) was measured in endothelium-intact and denuded pulmonary arteries (100- to 400-microm diameter). Pulmonary arterial production of the stable metabolites of thromboxane and prostacyclin was assessed in the presence and absence of NS-398. Dilation to arachidonic acid was greater for intact control than for intact hypoxic arteries, was unchanged by NS-398 in intact arteries of either group, and was augmented by NS-398 in denuded hypoxic arteries. ACh responses, which were dilation in intact control arteries but constriction in intact and denuded hypoxic arteries, were diminished by NS-398 treatment of all arteries. NS-398 reduced prostacyclin production by control pulmonary arteries and reduced thromboxane production by hypoxic pulmonary arteries. COX-2-dependent contracting factors, such as thromboxane, contribute to aberrant pulmonary arterial responses in piglets exposed to 3 days of hypoxia.     

高原鼠兔和昆明白小鼠肺组织结构比较

低氧性肺血管收缩反应钝化（blunted Hypoxic Pulmonary Vasoconstriction, bHPV）是高原鼠兔在进化过程中形成的对低氧环境的一种适应性策略。以胎儿期、幼龄期及成年期高原鼠兔和昆明白小鼠为研究对象,对两者的肺组织进行发育生物学、比较组织学和比较组织化学研究,以探讨高原鼠兔bHPV形成的组织形态学基础。结果表明：（1）高原鼠兔各时期肺组织微血管的双层弹性纤维含量均低于25%,无明显肌化现象;（2）高原鼠兔直径10~50 μm、50~100 μm和100~200 μm微血管的中膜肌层厚度与其外径比（MT/ED）随年龄增加而逐渐下降;成年高原鼠兔的肺组织微血管MT/ED10-50显著低于成年昆明白小鼠（P < 0.05）,但MT/ED50-100和MT/ED100-200均无明显的种间差异（P > 0.05）;（3）在直径10~50 μm直径范围微血管中,高原鼠兔和昆明白小鼠平滑肌细胞数与内皮细胞数的比值（SMC/EC）均随年龄增长呈上升趋势,且高原鼠兔SMC/EC的比值极显著低于同年龄组的昆明白小鼠（P < 0.01）。导致高原鼠兔bHPV发生的组织学基础可能是其肺组织中直径10~50μm微血管平滑肌细胞数量少。     

肺血管EDNO及其合酶在大鼠低氧性肺动脉高压形成中的作用

本研究观察了低氧对大鼠肺组织和血管内皮一氧化氮合酶（ＮＯＳ）活性及内皮衍生一氧化氮（ＥＤＮＯ）依赖性舒张反应的影响,以及ＮＯＳ抑制剂（Ｌ－ＮＡＭＥ）对常氧和低氧大鼠肺组织和血管内皮ＮＯＳ活性及颈、肺动脉血压（ＣＡＰｓ、ｍＰＡＰ）的作用。结果表明常氧大鼠肺泡内无肌性血管内皮未见ＮＯＳ活性,其肺血管床对ＥＤＮＯ依赖性舒血管物质ＢＫ没有反应,注射Ｌ－ＮＡＭＥ后大鼠ｍＰＡＰ略有降低,ＣＡＰｓ有所升高。低氧大鼠肺泡内无肌性血管内皮显示ＮＯＳ活性,对ＢＫ的ＥＤＮＯ依赖性舒张反应呈剂量依赖性增大,注射Ｌ－ＮＡＭＥ使低氧大鼠ｍＰＡＰ显著降低（Ｐ＜０．０１）,ＣＡＰｓ显著升高（Ｐ＜０．０５）。提示肺血管ＥＤＮＯ及其合酶在维持正常成年大鼠肺循环低压低阻中的生理作用值得进一步探讨;低氧引起肺血管内皮ｅｃＮＯＳ活性增加和ＥＤＮＯ生成增多可能起到限制肺动脉压过度升高的调制作用,也可能对肺血管内皮产生毒性作用,反而促进肺动脉高压的发生和发展。     

Optical Coherence Tomography of Pulmonary Arterial Walls in Humans and Pigs (Sus scrofa domesticus)

Pulmonary arterial hypertension (PAH) is a devastating disorder characterized by progressive elevation of the pulmonary pressures that, in the absence of therapy, results in chronic right-heart failure and premature death. The vascular pathology of PAH is characterized by progressive loss of small (diameter, less than 50 μm) peripheral pulmonary arteries along with abnormal medial thickening, neointimal formation, and intraluminal narrowing of the remaining pulmonary arteries. Vascular pathology correlates with disease severity, given that hemodynamic effects and disease outcomes are worse in patients with advanced compared with lower-grade lesions. Novel imaging tools are urgently needed that demonstrate the extent of vascular remodeling in PAH patients during diagnosis and treatment monitoring. Optical coherence tomography (OCT) is a catheter-based intravascular imaging technique used to obtain high-resolution 2D and 3D cross-sectional images of coronary arteries, thus revealing the extent of vascular wall pathology due to diseases such as atherosclerosis and in-stent restenosis; its utility as a diagnostic tool in the assessment of the pulmonary circulation is unknown. Here we show that OCT provides high-definition images that capture the morphology of pulmonary arterial walls in explanted human lungs and during pulmonary arterial catheterization of an adult pig. We conclude that OCT may facilitate the evaluation of patients with PAH by disclosing the degree of wall remodeling present in pulmonary vessels. Future studies are warranted to determine whether this information complements the hemodynamic and functional assessments routinely performed in PAH patients, facilitates treatment selection, and improves estimates of prognosis and outcome.Abbreviations: OCT, optical coherence tomography; PAC, pulmonary artery catheter; PAH, pulmonary arterial hypertensionPulmonary arterial hypertension (PAH) is a devastating disorder characterized by progressive elevation of pulmonary pressures that, when untreated, can lead to chronic right heart failure and death.¹⁴ The vascular pathology of PAH is characterized by neointimal formation, medial thickening, intravascular thrombi and, in severe cases, intravascular clusters of disorganized endothelial cells that give rise to tortuous endovascular channels.⁸ Most of the early vascular lesions are found in small (diameter, less than 50 μm) pulmonary arteries. However, as the disease advances, pulmonary arteries (diameter, 50 μm or larger) proximal to these lesions also display evidence of luminal narrowing and medial thickening.^7,8,15 Most patients with PAH are younger than those with chronic systemic vascular disorders (that is, coronary artery disease, peripheral vascular disease, systemic hypertension), whose vascular pathology involves mostly large to medium-sized arteries. However, both patient populations demonstrate various pathologic features, including vascular smooth-cell accumulation, neointimal formation, inflammation, luminal narrowing, and alterations in the composition of the extracellular matrix.^6,17The only definite way to diagnose PAH is through right heart catheterization to directly measure the pressure in the pulmonary circulation. Although pulmonary angiography during right heart catheterization cannot be used to diagnose PAH, it provides supportive evidence of PAH by demonstrating significant peripheral small vessel loss and luminal narrowing in the remaining central vessels. Angiography can help clinicians visualize pulmonary vessels in real time, but this diagnostic technique has important limitations. The use of ionized contrast can cause allergic reactions and may trigger acute renal failure due to contrast-induced nephropathy.²⁶ In addition, pulmonary angiography provides information regarding gross vessel appearance and small vessel perfusion but not about the state of vascular wall remodeling or the extent of luminal narrowing associated with PAH at any stage.^5,16 Therefore, imaging techniques are urgently needed that complement the hemodynamic information obtained via right heart catheterization with a safe and reproducible method to assess vascular wall pathology, thereby allowing clinicians to correlate the clinical evolution of PAH with the progression of vascular pathology.The last decade has seen tremendous progress in the development of intravascular imaging modalities that can identify patients at risk for developing complications related to systemic vascular disease and therefore prevent disease-related morbidity and mortality.⁴ One such modality is optical coherence tomography (OCT), an imaging technique that uses a thin (diameter, 1.0 mm) wire and near-infrared light to capture micrometer-resolution, 3D images from within optical scattering media (for example, biologic tissue).¹ Superior to other intravascular imaging techniques, OCT is frequently used in patients with coronary artery disease, where it provides high-resolution images of the coronary arterial wall that correlate highly with pathology seen in explanted vessels.^10,11,21 To date, several small studies have demonstrated the application of OCT to the evaluation of vascular remodeling in both idiopathic PAH and chronic thromboembolic PAH.^7,21 However, despite OCT''s obvious advantages in the characterization of vascular remodeling in discrete segments of the pulmonary circulation, whether OCT provides anatomic information across the length of the pulmonary artery has not been tested.Here, we report the capacity of OCT to obtain both longitudinal and cross-sectional images that provide accurate anatomic information on healthy pulmonary arteries in explanted human lungs and during the pulmonary arterial catheterization of a live adult pig (Sus scrofa domesticus).     

Perinatal history of hypoxia leads to lower vascular pressures and hyporeactivity to angiotensin II in isolated lungs of adult rats

The most dramatic changes in pulmonary circulation occur at the time of birth. We hypothesized that some of the effects of perinatal hypoxia on pulmonary vessels are permanent. We studied the consequences of perinatal exposure to hypoxia (12 % O2 one week before and one week after birth) in isolated lungs of adult male rats (approximately 12 weeks old) perfused with homologous blood. Perfusion pressure-flow relationship was tilted towards lower pressures in the perinatally hypoxic as compared to the control, perinatally normoxic rats. A non-linear, distensible vessel model analysis revealed that this was due to increased vascular distensibility in perinatally hypoxic rats (4.1 +/- 0.6 %/mm Hg vs. 2.3 +/- 0.4 %/mm Hg in controls, P = 0.03). Vascular occlusion techniques showed that lungs of the perinatally hypoxic rats had lower pressures at both the pre-capillary and post-capillary level. To assess its role, basal vascular tone was eliminated by a high dose of sodium nitroprusside (20 microM). This reduced perfusion pressures only in the lungs of rats born in hypoxia, indicating that perinatal hypoxia leads to a permanent increase in the basal tone of the pulmonary vessels. Pulmonary vasoconstrictor reactivity to angiotensin II (0.1-0.5 microg) was reduced in rats with the history of perinatal-hypoxia. These data show that perinatal hypoxia has permanent effects on the pulmonary circulation that may be beneficial and perhaps serve to offset the previously described adverse consequences.     

Reactive oxygen species from NADPH oxidase contribute to altered pulmonary vascular responses in piglets with chronic hypoxia-induced pulmonary hypertension

Our main objective was to determine whether reactive oxygen species (ROS), such as superoxide (O(2)(-)) and hydrogen peroxide (H(2)O(2)), contribute to altered pulmonary vascular responses in piglets with chronic hypoxia-induced pulmonary hypertension. Piglets were raised in either room air (control) or hypoxia for 3 days. The effect of the cell-permeable superoxide dismutase mimetic (SOD; M40403) and/or PEG-catalase (PEG-CAT) on responses to acetylcholine (ACh) was measured in endothelium-intact and denuded pulmonary resistance arteries (PRAs; 90-to-300-microm diameter). To determine whether NADPH oxidase is an enzymatic source of ROS, PRA responses to ACh were measured in the presence and absence of a NADPH oxidase inhibitor, apocynin (APO). A Western blot technique was used to assess expression of the NADPH oxidase subunit, p67phox. A lucigenin-derived chemiluminescence technique was used to measure ROS production stimulated by the NADPH oxidase substrate, NADPH. ACh responses, which were dilation in intact control arteries but constriction in both intact and denuded hypoxic arteries, were diminished by M40403, PEG-CAT, the combination of M40403 plus PEG-CAT, as well as by APO. Although total amounts were not different, membrane-associated p67phox was greater in PRAs from hypoxic compared with control piglets. NADPH-stimulated lucigenin luminescence was nearly doubled in PRAs from hypoxic vs. control piglets. We conclude that ROS generated by NADPH oxidase contribute to the aberrant pulmonary arterial responses in piglets exposed to 3 days of hypoxia.