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

Abstract

Schwenke DO, Pearson JT, Umetani K, Kangawa K, Shirai M. Imaging of the pulmonary circulation in the closed-chest rat using synchrotron radiation microangiography. J Appl Physiol 102: [787][788][789][790][791][792][793] 2007. First published October 12, 2006; doi:10.1152/japplphysiol.00596.2006.-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 Ͻ 200 m), 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% O 2 for 4 min each) pulmonary vasoconstriction (HPV). Using SR we were able to visualize pulmonary microvessels with a diameter of Ͻ100 m (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 m. The greatest degree of pulmonary vasoconstriction was observed in vessels with a diameter between 200 and 300 m. 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. pulmonary microvessels; hypoxia; intact chest STRUCTURAL AND FUNCTIONAL changes of the pulmonary circulation, particularly during the pathogenesis of pulmonary arterial hypertension (PAH), remain to be fully elucidated. Specifically, the small peripheral pulmonary arteries (Ͻ500 m) are believed to be most susceptible to structural changes during, for example, chronic exposure to hypoxia (1,6,7,15,19,32).To date, most small-animal studies that have described the anatomic geometry of the pulmonary circulation have been limited to the use of in vitro or ex vivo preparations. While such data have aided our understanding concerning the pulmonary microcirculation, such invasive procedures ultimately disrupt the natural physiological milieu of the lung. Ideally, a technique of visualizing the pulmonary circulation within a closed-chest model, i.e., under intact neurohumoral regulation, is required to fully understand the structural and functional properties of the microcirculation in the normal lung as well as understand the dynamic changes that occur in pathologic...

BMP4 Increases Canonical Transient Receptor Potential Protein Expression by Activating p38 MAPK and ERK1/2 Signaling Pathways in Pulmonary Arterial Smooth Muscle Cells

“…Although both proximal and distal PAs undergo profound remodeling during the development of CHPH, their structural changes and the underlying cellular and molecular mechanisms appear to be different (20). The distal PAs are considered to be more important than the proximal PAs in the pathogenesis of CHPH, because the distal small peripheral pulmonary arteries are more susceptible to structural changes during chronic exposure to hypoxia (21)(22)(23)(24), and they constitute the primary site of hypoxic pulmonary vasoconstriction (HPV) in the pulmonary vasculature (25). During many years of effort to elucidate the mechanisms of differential remodeling properties and differential HPV responses of proximal and distal PAs, many discrepancies between proximal and distal PASMCs have been explored, such as their proliferative responses to various growth factors (e.g., platelet-derived growth factor, angiotensin II, and transforming growth factor-b1) and hypoxia (26), the hypoxiainduced changes in [Ca 21 ] i (27), the distribution of inositol 1,4,5-trisphosphate and ryanodine receptors in sarcoplasmic reticulum Ca 21 stores (28), and the expression level and function of voltage-gated potassium channels and SOCCs (17,29).…”

Contrast angiography of the rat renal microcirculation in vivo using synchrotron radiation

“…Microangiography using synchrotron radiation has recently been applied to a range of vascular beds (27), including the liver (14), lungs (25,26), brain (13, 18 -20, 30), and heart (12). One of the major the strengths of the technique is that there is no geometric magnification of vessels.…”

“…One of the major the strengths of the technique is that there is no geometric magnification of vessels. The highly collimated X-ray beam, the small X-ray source, and the long distance between the source and the kidney result in insignificant magnification of blood vessels due to their relative position within the organ of interest (i.e., ϫ1.004) (26). As for other vascular imaging modalities (34), analysis of microangiograms assumes all arterial vessel segments are cylindrical in shape.…”

Enhancement of myofilament calcium sensitivity by acute hypoxia in rat distal pulmonary arteries

“…The identities of these factors remain unknown; however, antagonists of endothelin-1 (ET-1) had no effect on phase 2 HPV in endothelium-intact IPA, suggesting that ET-1 played no role (51). Although the nitric oxide/guanylate cyclase/protein kinase G (NO/GC/PKG) transduction pathway can alter Ca 2ϩ sensitivity in pulmonary arteries (27, 57), its effect on Ca 2ϩ sensitivity during acute hypoxia has not been examined.Consistent with endothelium dependence, hypoxia did not change steady-state isometric force achieved during normoxia at [Ca 2ϩ ] i ϭ 3-1,000 nM in endothelium-denuded rat extrapulmonary arteries permeabilized with ␤-escin and exposed to phorbol-12,13-dibutyrate, a protein kinase C activator, at 30°C (58); however, an effect of hypoxia may have been precluded in these experiments by use of proximal pulmonary arteries, which have weak contractile responses to hypoxia (39,40,61,65); phorbol-12,13-dibutyrate, which enhances Ca 2ϩ sensitivity on its own (30, 59); and low temperature, which inhibits HPV (4,21,36). Hypoxia also did not alter the relation between increases in [Ca 2ϩ ] i and decreases in cell length induced by the Ca 2ϩ ionophore 4-bromo-A-23187 in freshly isolated porcine distal PASMC at 37°C (62); however, since these cells were variably attached to glass coverslips, uneven loading among cells and the absence of isotonic conditions may have obscured possible effects of hypoxia.…”