Hydraulic conductance of lung endothelial phenotypes and Starling safety factors against edema

Recent permeability studies comparing endothelial cell phenotypes derived from alveolar and extra-alveolar vessels have significant implications for interpreting the mechanisms of fluid homeostasis in the intact lung. These studies indicate that confluent monolayers of rat pulmonary microvascular endothelial cells had a hydraulic conductance (L(p)) that was only 5% and a transendothelial flux rate for 72-kDa dextran only 9% of values determined for rat pulmonary artery endothelial cell monolayers. On the basis of previous studies partitioning the filtration coefficients between alveolar and extra-alveolar vascular segments in rat lungs and previous studies of lymph albumin fluxes and permeability, the contribution of the alveolar capillary segment to total albumin flux in lymph was estimated to be less than 10%. In addition, the Starling safety factors against the edema calculated for the alveolar capillaries are quite different from those estimated for whole lung. Estimates of the edema safety factor due to increased filtration across the alveolar capillary wall based on the low L(p) indicate it is quantitatively the greatest safety factor, although it would be a minor safety factor for extra-alveolar vessels. Also, a markedly higher effective protein osmotic absorptive force for plasma proteins must occur in the capillaries relative to extra-alveolar vessels. The lower L(p) for alveolar capillaries also has implications for the sequence of hydrostatic edema formation, and it also may have a role in preventing exercise-induced alveolar flooding.     

Status of the capillary endothelium of the lung in normovolemic perfusion of the organ through the system of the pulmonary artery

Pulmonary perfusion for 30 min to the dog under conditions of normovolemia is not accompanied with any essential changes in parameters of alveolar capillaries endothelium. Just the opposite, transformation of endothelial lining of the peribronchial capillaries demonstrates possible disturbances of the liquor transport across the walls of these vessels. The volumetric part of the interstitial space near these capillaries increases, while in the alveolar septa it does not change. In lymph formation, flowing out of the lung, together with bronchial capillaries, blood capillaries of the alveoli must take part.     

Scanning electron microscope study of the liver microcirculation

During the experimental investigation performed in dogs and rats, by means of scanning electron microscopy of corrosive anatomical preparations, the spatial organization of all parts of the hepatic vascular bed (arterial, venous and lymphatic) has been studied, specific features of their components construction have been described. Within the limits of one hepatic lobule the number of vessels included in the portal vein system exceeds that of the arterial ones, originating from the proper hepatic artery system. In every part of the vascular bed the gradient of the form, orientation and pronouncement of the nuclei-containing zones in endotheliocytes and myocytes has been established. Various appliances participating in the blood and lymph stream regulation in different parts of the vascular bed have been revealed. As initial elements of the lymph bed, closed digital or loop-like capillaries should be regarded, they localize in the organ's connective tissue framework. Around the portal and hepatic veins and their branches, as well as around the biliary ducts, well developed plexuses of the lymphatic and blood capillaries and vessels localize, they are the main draining pathways of the organ. The degree of development and pronouncement of these plexuses depends on the lumen size in the formation they accompany.     

Localization of VIP-immunoreactive nerves in airways and pulmonary vessels of dogs,cats, and human subjects

Summary VIP-containing neurons were localized in lungs from dogs, cats, and human subjects by means of the indirect immunofluorescence technique. Nerve fibers and terminals were observed in the smooth muscle layer and glands of airways, and within the walls of pulmonary and bronchial vessels, especially at the medial-adventitial junction. VIP-positive nerve cell bodies were identified in ganglia located in the walls of bronchi. These findings provide an anatomic basis for the possible modulation of airway and pulmonary vascular function by this neuropeptide.Supported by National Research Service Award HL 5914 and by Lung Center Award HL 14187 from NHLBI, USPHS     

Effect of sensory neuropeptides on canine bronchial and pulmonary vessels in vitro

Sensory neuropeptides may be important in the noncholinergic component of parasympathetic vasodilation in the tracheobronchial circulation. We studied the effects of substance P (SP), neurokinin A (NKA), neurokinin B (NKB) and calcitonin gene-related peptide (CGRP) on the isolated canine bronchial artery and used pulmonary artery and vein of similar size for comparison. CGRP (10pM-300nM) was a potent relaxant of the bronchial and pulmonary arteries, and the pulmonary vein with equal potency in all vessels. SP in low concentrations (10pM-100nM) caused vasodilation of the precontracted bronchial artery and in high concentration (10-100 microM) contracted the vessel from resting tone. SP also relaxed the pulmonary artery and vein. NKA and NKB caused relaxation in all three vessels. All of the vascular effects of the sensory neuropeptides were concentration-dependent. The order of potency of the neuropeptides in the bronchial and pulmonary artery was SP greater than NKA greater than CGRP greater than NKB. In the pulmonary vein NKB caused a much larger relaxation than SP and NKA but it was less potent than either NKA or CGRP. Capsaicin (1 microM) caused a large contraction of the bronchial artery, similar in magnitude to the contraction caused by high dose of SP. Neuropeptide Y was also studied and found to cause no consistent constriction of any of the vessels studied. In conclusion, CGRP is a universal dilator of the bronchial and pulmonary blood vessels. SP and NKA exert their main effect on arterial vasomotor tone, whereas NKB is the only tachykinin producing marked dilation of the pulmonary vein.     

Topography of lymphatic collectors and regional lymph nodes of the canine heart and their morphological characteristics

In 40 dogs lymphatic vessels and regional lymph nodes of the heart have been prepared. Morphology of the regional lymph nodes have been studied by means of various histological techniques. Lymph outflow from the canine ventricles is realized by three (less often), or by two (more often) collectors. In very rare cases one collector is formed. From the right atrium lymph flows out in two collectors (cranial and left). Lymphatic vessels of the left atrium get into the left collector of the ventricles, or into the tracheobronchial lymph nodes. Into the same nodes gets the lymphatic vessel, forming at the border of the left and right atrii. Cranial, medial, caudal mediastinal nodes (lymphatic mediastinal system) and right, middle and left tracheobronchial lymph nodes (tracheobronchial system) are regional lymph nodes of the canine heart. In the lymph nodes of the tracheobronchial system of puppies older than one month presence of exogenic pigment and signs of fibrous degeneration of parenchyma are noted.     

Structure and function of lymphatic postcapillaries (coordinating mechanism of the processes of interstitial transport and lymphatic resorption

Investigation performed on topography, structure and resorptive function of lymphatic microvessels in the serous membranes gives possibilities to work out a model on formation and transport of lymph. Lymphatic postcapillaries (LP) - thin-walled endothelial channels with valves make an important link of the lymphatic system. The LP structure is similar to that of capillaries. These microvessels are situated in the interstitial space area, that are characterized with their high content of plasma proteins and water. Interrelation in concentrations of protein in the LP lumen and in the tissue ensures the existence of the osmotic gradient pressure through the wall and contributes liquor resorption into the lumen of microvessels. Peritoneal lymphatic capillaries are situated in the areas of a higher hydrotation level of the interstitial space. They can control the rate of the liquor filtration from plasma into tissue and regulate the resorption level in the whole lymphatic network. The model provides a differentiated participation of the LP and capillaries in performing resorption of proteins and liquor from the interstitium. The resorption mechanisms are closely connected with processes of the lymph movement along the vessels.     

Reflex cardiorespiratory responses to pulmonary vascular congestion

The purpose of these studies was to determine the reflex responses of the cardiovascular system and central inspiratory activity caused by pulmonary vascular congestion. We used a canine preparation in which the left lung was isolated in situ and could be exposed to a variety of stimuli, including distension of the pulmonary capillaries with blood, without direct mechanical or chemical alterations on the circulation. We found that lung expansion to 30 cmH2O and stimulation of nerve endings of the left lung with capsaicin caused pronounced transient reflex bradycardia (-30 to -50 beats/min) and hypotension (-25 to -40 mmHg) and caused reflex cessation of inspiratory activity. Pressurizing the left pulmonary vessels by injecting blood in volumes sufficient to raise pulmonary transcapillary pressures to 30 mmHg caused no changes in heart rate, systemic arterial pressure, or inspiratory muscle activity. These results lead us to conclude that pulmonary vascular congestion does not stimulate pulmonary C-fibers or any other nerve endings to such a degree as to cause detectable changes in blood pressure, heart rate, or central inspiratory activity. Morphometric analysis revealed distended capillaries engorged with blood, but the alveolar wall surface area was not increased which raises the possibility that expansion of the alveolar membrane may be needed to mechanically initiate the C-fiber reflex.     

Effect of isoproterenol or exercise on pulmonary lymph flow and hemodynamics

Experiments were performed to determine whether different methods of increasing cardiac output would have similar effects on lung lymph flow, and to assess the contribution of the microvasculature (fluid-exchanging vessels) to the total calculated pulmonary vascular resistance. Yearling unanesthetized sheep with chronic vascular catheters and lung lymph fistulas underwent intravenous infusions of isoproterenol at 0.2 micrograms X kg-1. min-1 (n = 8) or were exercised on a treadmill (n = 16). Both isoproterenol and exercise increased cardiac output, lowered calculated total pulmonary and systemic vascular resistances, and had no effect on the calculated pulmonary microvascular pressure. Isoproterenol infusions did not affect lung lymph flow, whereas exercise increased lung lymph flow in proportion to the increase in cardiac output. We conclude that 1) the sheep has a different pulmonary hemodynamic response to exercise than dogs and man, 2) the microvasculature is recruited during exercise-induced but not isoproterenol-induced increases in cardiac output, and 3) the microvasculature represents only a small proportion of the total calculated pulmonary vascular resistance.     

Electron microscopic characteristics of plant peroxidase transport pathways in the microcirculatory bed of the rabbit peritoneum

The dynamics of exogenic peroxidase transfer from blood into the roots of the rabbit mesenteric lymphatic system have been studied by means of electron microscopic methods in combination with the trasser technique. Light optic identification of the vascular segments and selection of samples for electron microscopic analysis make it possible to reveal certain differences in the pathways of protein transport via the walls of the blood capillaries and venules. The vesicular transport is the only means for peroxidase to be transferred via the walls of the mesenteric blood capillaries. The time for transendothelial transfer of the marker is more than 10 min. In the venules the vesicular transport of protein does not differ from that in the capillaries, however, the predominant leakage of peroxidase from blood into the interstitium is performed through open interendothelial contacts. The hemato-interstitial transport via the intercellular clefts takes less than 3 min. For transferring protein from the interstitium into the lumen of the lymphatic capillaries and postcapillaries, the vesicular mechanism is used, and to a less extent--the open intercellular contacts. A suggestion is made that the term "open contact" should be understood in functional meaning and this means should be considered as an intercellular pathway for transporting molecules of a definite size.     

Application of respiratory heat exchange for the measurement of lung water.

A noninvasive method for measuring pulmonary blood flow and lung mass (called airway thermal volume), based on the measurements of lung heat exchange with environment, is described. The lungs function as a steady-state heat exchange system, having an inner heat source (pulmonary blood flow) and an external heat sink (ventilation). Sudden changes in the steady-state condition, such as caused by hyperventilation of dry air, lead to a new steady state after a few minutes. The expired air temperature difference between the initial and final steady states is proportional to pulmonary blood flow, whereas the rate at which the new steady state is achieved is proportional to airway thermal volume. The method was tested in 20 isolated dogs lungs, 9 perfused goat lungs, and 27 anesthetized sheep. The expired air temperature fall during hyperventilation was inversely proportional to the perfusion rate of the isolated lungs, and half-time of the temperature fall was proportional to the lung tissue mass. Experiments in anesthetized sheep showed that the measured airway thermal volume is close to the total mass of the excised lungs, including its residual blood (r = 0.98). Pulmonary edema and fluid instillation into the bronchial tree increased in the measured lung mass.     

Vascular effects of platelet-activating factor in lambs: role of cyclo- and lipoxygenase.

In adult sheep, platelet-activating factor (PAF) effects include systemic hypotension and pulmonary hypertension. To identify developmental differences in vascular responses to PAF, we studied the effects of C18- and C16-PAF in 49 +/- 2- (SE) day-old lambs. Responses of upstream (arteries and microvessels) and venous segments of the lung to C18-PAF were determined both in vivo and in isolated lungs. In isolated lungs, the role of eicosanoids in PAF effects was also determined. In vivo, both C18- and C16-PAF caused a significant increase in systemic and pulmonary vascular resistance. The magnitude of vascular responses to C16-PAF was greater than that to C18-PAF. C18-PAF constricted both upstream and venous segments of the pulmonary circulation. Cyclooxygenase inhibition in isolated lungs attenuated arterial constriction to C18-PAF, whereas simultaneous cyclooxygenase and lipoxygenase inhibition completely blocked the effects of C18-PAF. In summary, in contrast to PAF effects in adult sheep, PAF constricts both systemic and pulmonary vessels in lambs, with significant pulmonary venous constriction. Eicosanoids, especially lipoxygenase products, play a major role in mediating PAF effects in the lung.     

Lymphatic and blood vessels of the liver in acute and chronic cholecystitis]

Changes in lymph and blood vessels were studied in 110 dogs with acute and chronic cholecystitis. It was established that in the period of development of acute inflammatory processes in the gall bladder the monolayer network of hepatic capillaries was changed into bi-layer, took place the formation of plane networks at the side of the lobule and lacunary dilatations in the site of fusion of lymph capillaries, dilatation and deformation of lymph capillaries and vessels. Under conditions of chronic cholecystitis fibrosis and sclerosis of the portal tracts were accompanied by intensive growth (and reduction - in parallel) of lymph capillaries. Thick small-looped network was observed to develop around false lobules during development of cyrrhosis. A conclusion is made that early cholecystectomy is necessary in cases of inflammatory diseases of the gallbladder.     

Vascular reactivity is increased in rat lungs injured with alpha-naphthylthiourea

We investigated the effects of lung injury due to alpha-naphthylthiourea (ANTU) on pulmonary vascular reactivity. Rats were treated with ANTU (10 mg/kg ip) or the vehicle Tween 80. Four hours later, lungs from ANTU-treated rats had increased wet-to-dry weight ratios, bronchial lavage protein concentrations, and perivascular edema. To test vascular reactivity, lungs were isolated and perfused with blood at constant flow rate, while mean pulmonary arterial pressure was monitored. ANTU-treated lungs vasoconstricted earlier than Tween-treated lungs in response to severe airway hypoxia (fractional inspired O2 0%). ANTU-treated lungs vasoconstricted in response to 10% O2, while Tween-treated lungs failed to respond to 10% O2, indicating that the threshold for hypoxic vasoconstriction was decreased by ANTU. ANTU also decreased the threshold for and increased the magnitude of angiotensin II pressor responses, indicating that the increased vasoreactivity was not specific for hypoxia. Addition of meclofenamate to perfusates increased the rate and magnitude of responses to 0% O2 in Tween-treated lungs, but did not change the responses of ANTU-treated lungs. Light microscopy of ANTU-treated lungs showed no pulmonary arterial obstruction, and electron microscopy revealed mild capillary endothelial cell injury. We conclude that enhanced pulmonary vascular reactivity accompanies the increased-permeability pulmonary edema caused by ANTU. A similar increase in vasoreactivity might contribute to pulmonary hypertension observed in patients with the adult respiratory distress syndrome.     

Structural interrelations of the air-blood barrier and terminal sections of the lymphatic link in the pulmonary microcirculatory bed in chronic hypervolemia

The interalveolar septa of the human lungs are known to have no lymphatic capillaries. The topography of the pulmonary lymphatic system origin under conditions of chronic hypervolemia is still not investigated. Lungs of 24 corpses of persons, died from non-pulmonary pathology (control) and lungs of 34 corpses of persons, died from congenital and acquired heart disease accompanied with pre- and postcapillary forms of the pulmonary circulation hypertension, have been investigated. Decreased efficiency of the microcirculation, increased permeability of the blood capillary walls against the background of hypoxia result in an elevated production of lymph. Intensified collagen formation in the blood vessel walls and in the interalveolar septa is the prerequisite for reorganization of the pulmonary lymphatic bed. Lymphatic capillaries are found to grow into some sclerotic interalveolar septa and into deep structures of the blood capillary walls. This demonstrates a high plasticity of the lymphatic link terminal parts of the microcirculatory bed in pathologically changed lungs.     

Determination of circulation disturbance in the rat lungs in modelling of chronic obstructive disease

Development of chronic obstructive pulmonary disease (COPD) involves not only the bronchial and respiratory areas of the lungs, but also the system of pulmonary circulation, which begins with the defeat of capillary blood flow. One of radiological methods of studying lung microcirculatory functions is perfusion scintigraphy. We designed the technique of radiological examination and identified its abilities in determination of the role of vascular dysfunctions in experimental model of development of COPD. We assessed the results of pharmacological agents that affect the microcirculatory bed of the lungs and smooth muscles of pulmonary arteries in rats. Studies have shown the promise of the possibility of using the drug sulodexide for studying impaired endothelial function in clinical practice.     

Flow through zone 1 lungs utilizes alveolar corner vessels

We have previously observed flows equivalent to 15% of the resting cardiac output of rabbits occurring through isolated lungs that were completely in zone 1. To distinguish between alveolar corner vessels and alveolar septal vessels as a possible zone 1 pathway, we made in vivo microscopic observations of the subpleural alveolar capillaries in five anesthetized dogs. Videomicroscopic recordings were made via a transparent thoracic window with the animal in the right lateral position. From recordings of the uppermost surface of the left lung, alveolar septal and corner vessels were classified depending on whether they were located within or between alveoli, respectively. Observations were made with various levels of positive end-expiratory pressure (PEEP) applied only to the left lung via a double-lumen endotracheal tube. Consistent with convention, flow through septal vessels stopped when PEEP was raised to the mean pulmonary arterial pressure (the zone 1-zone 2 border). However, flow through alveolar corner vessels continued until PEEP was 8-16 cmH2O greater than mean pulmonary arterial pressure (8-16 cm into zone 1). These direct observations support the idea that alveolar corner vessels rather than patent septal vessels provide the pathway for blood flow under zone 1 conditions.     

Lymph flow from edematous dog lungs

We measured the flow rate (QLV) from cannulated lung lymph vessels in anesthetized dogs. Low-resistance lymph cannulas were used and the vessels were cannulated at the lung hilus. When we increased left atrial pressure to 42.9 +/- 5.7 (SD) cmH2O (base line = 6.6 +/- 4.6 cmH2O), the lungs became edematous and QLV increased from a base line of 20.4 +/- 21.5 microliters/min to 388 +/- 185 microliters/min. QLV plateaued at the higher level. We also measured the relationship between lymph flow rate and the height of the outflow end of the lymph cannula. From this relationship, determined at the end of the period of elevated left atrial pressure, we calculated the effective resistance and pressure driving lymph from the lungs. We also cannulated lymph vessels in the downstream direction and estimated the effective resistance and pressure opposing flow into the part of the lymphatic system between the lung hilus and the veins (extrapulmonary lymph vessels). We found that the effective resistance of the extrapulmonary part of the lymph system (0.042 +/- 0.030 (SD) cmH2O X min X microliter-1) was large compared with the resistance of the lymph vessels from the lungs (0.026 +/- 0.027). These data indicate that the resistance of the extrapulmonary part of the lung lymph system limits the maximum flow of lymph from edematous lungs.     

Spontaneous bronchopneumonia in laboratory dogs infected with untyped Mycoplasma spp

Three Mycoplasma spp. were isolated from five colony bred laboratory dogs (Canis familiaris) obtained from a single vendor. Four of these animals were Beagles and one was a mongrel. Three displayed clinical signs of respiratory disease including dyspnea, chronic coughing and moist rales, while the other two dogs were observed during thoracic surgery to have macroscopic lesions suggestive of pneumonia. All five dogs were submitted for diagnostic necropsy during which they were cultured for bacteria and mycoplasma. Mycoplasma spp. having three distinct colonial forms were isolated from the lungs of each of the animals. These three isolates were sent to the National Cancer Institute Diagnostic Microbiology Laboratory and to the National Institutes of Health, NIAID, Mycoplasmology Laboratory. Neither laboratory could serotype these isolates against antisera to 73 Mycoplasma spp., including the common canine mycoplasmas, and nine Acholeplasma spp. Histologically, the bronchopneumonia was characterized by bronchiectasis, purulent bronchiolitis, bronchial and bronchiolar epithelial hyperplasia, chronic non-suppurative peribronchiolitis and perivasculitis, bronchiolitis obliterans, and acute to subacute purulent pneumonia. The similarity between the pathologic findings in these animals and those observed in respiratory mycoplasmosis of other species, e.g. the rat, suggests a causal relationship between the isolated mycoplasmas and the pulmonary disease observed in these dogs.