No abstract

Lung parenchyma is normally considered to be isotropic, that is, its properties do not depend upon specific preferential directions. The assumption of isotropy is important for both modeling of lung mechanical properties and quantitative histologic measurements. This assumption, however, has not been previously examined at the microscopic level, in part because of the difficulty in large lungs of obtaining sufficient numbers of small samples of tissue while maintaining the spatial orientation. In the mouse, however, this difficulty is minimized. We evaluated the parenchymal isotropy in mouse lungs by quantifying the mean airspace chord lengths (Lm) from high-resolution histology of complete sections surrounded by an intact continuous visceral pleural membrane. We partitioned this lung into 5 isolated regions, defined by the distance from the visceral pleura. To further evaluate the isotropy, we also measured Lm in two orthogonal spatial directions with respect to the section orientation, and varied the sample line spacing from 3 to 280 μm. Results show a striking degree of parenchymal anisotropy in normal mouse lungs. The Lm was significantly greater when grid lines were parallel to the ventral–dorsal axis of the tissue. In addition the Lm was significantly smaller within 300 μm of the visceral pleura. Whether this anisotropy results from intrinsic structural factors or from nonuniform shrinkage during conventional tissue processing is uncertain, but it should be considered when interpreting quantitative morphometric measurements made in the mouse lung.

We have shown that left pulmonary artery ligation (LPAL) in mice causes a prompt angiogenic response, with new systemic vessels from intercostal arteries penetrating the pleura within 6 days. Because angiogenic vessels in other organs have been shown to exhibit increased permeability, we studied vascular permeability (Evans blue dye extravasation, lung wet weight-to-dry weight ratio, and lavaged protein) in naive C57BL/6 mice and 4 h, and 14 and 21 days after LPAL (4 -6 mice/time point). We also measured radiolabel clearance as an index of functional perfusion after LPAL. Tracer clearance from the left lung was maximal by 6 days after LPAL and not different from right lungs. Thus a functional vasculature is established before 6 days of LPAL that results in normal tracer clearance. By 21 days after LPAL, Evans blue-albumin was significantly increased in the left lung relative to both 4 h (no vasculature) and 14 days after LPAL. Only after 21 days of LPAL was left lung wet weight-to-dry weight ratio significantly different from naive lungs. Additionally, lavaged protein was significantly increased both 4 h and 21 days after LPAL relative to control mice. Thus, using three different methods, results consistently demonstrated increased permeability to protein and water 21 days after LPAL. Although changes in surface area of perfusion might affect the interpretation of these results, blood flow measured with labeled microspheres indicated no change in left lung perfusion between 14 and 21 days of LPAL. Thus the lung vasculature, remodeled as a consequence of chronic pulmonary artery obstruction, demonstrates increased water and protein permeability.angiogenesis; bronchoalveolar lavage; Evans blue dye; lung wet weight-to-dry weight ratio; mice; technetium-99m-labeled diethylenetriamine pentaacetic acid CHRONIC PULMONARY ISCHEMIA leads to angiogenesis involving systemic arteries that proliferate and anastomose with the pulmonary vasculature. Neovascularization of the systemic circulation in the lung after chronic pulmonary artery obstruction has been demonstrated in the human (5), sheep (1), dog (10), pig (7), rabbit (18), guinea pig (17), rat (20), and mouse (13). In most models, there is rapid growth of the bronchial circulation as well as other systemic thoracic arteries. Bronchial blood flow in the sheep was shown to increase fivefold by 3 wk after left pulmonary artery ligation (LPAL) (1). After 4 mo of left pulmonary artery obstruction in dogs, systemic blood flow to the left lower lobe increased from 5 to 330 ml/min (11). Despite these dramatic changes in the perfusion of the lung, little information exists to establish that these new vascular networks function normally. In systemic organs as well as tumors, angiogenic vessels are known to exhibit increased vascular permeability (9). One of the few studies focused on determining vascular barrier properties after chronic pulmonary artery ligation demonstrated increased lung vascular permeability; however, changes were measured after reperfusion of the obstructed ...

In ovine cerebral arteries, adrenergic-mediated vasoconstrictor responses differ significantly with developmental age. We tested the hypothesis that, in part, these differences are a consequence of altered alpha(2)-adrenergic receptor (alpha(2)-AR) density and/or affinity. In fetal (approximately 140 days) and adult sheep, we measured alpha(2)-AR density and affinity with the antagonist [(3)H]idazoxan in main branch cerebral arteries and other vessels. We also quantified contractile responses in middle cerebral artery (MCA) to norepinephrine (NE) or phenylephrine in the presence of the alpha(2)-AR antagonists yohimbine and idazoxan and contractile responses to the alpha(2)-AR agonists clonidine and UK-14304. In fetal and adult cerebral artery homogenates, alpha(2)-AR density was 201 +/- 18 and 52 +/- 6 fmol/mg protein, respectively (P < 0.01); however, antagonist affinity values did not differ. In fetal, but not adult, MCA, 10(-7) M yohimbine significantly decreased the pD(2) for NE-induced tension in the presence of 3 x 10(-5) M cocaine, 10(-5) M deoxycorticosterone, and 10(-6) M tetrodotoxin. In fetal, but not adult, MCA, UK-14304 induced a significant decrease in pD(2) for the phenylephrine dose-response relation. In addition, stimulation-evoked fractional NE release was significantly greater in fetal than in adult cerebral arteries. In the presence of 10(-6) M idazoxan to block alpha(2)-AR-mediated inhibition of prejunctional NE release, the fractional NE release was significantly increased in both age groups. We conclude that in fetal and adult ovine cerebral arteries, alpha(2)-AR appear to be chiefly prejunctional. Nonetheless, the fetal cerebral arteries appear to have a significant component of postjunctional alpha(2)-AR.

There was no sustained decrease in CBF after ligation of either the carotid artery or jugular vein. Venoarterial but not venovenous ECMO induced decreases of CBF that could not be attributed to changes in blood gases or blood pressure but that may relate to diminished pulsatility in cerebral resistance vessels or to differences in levels of circulating vasoactive compounds.