Rat Lung Parenchyma Research Articles

Persistence of long, thin chrysotile asbestos fibers in the lungs of rats.

The distribution of inhaled mineral fibers in the lung determines the site and severity of disease caused by the fibers. Some of our recent work has described the fate of inhaled asbestos fibers in rodents. After a brief inhalation exposure, asbestos fibers are deposited primarily at the first alveolar duct bifurcations, and fibrotic lesions are initiated. These sites of deposition occur as close to the visceral pleura as 220 micron. Several studies have suggested that short fibers are cleared from the lung more efficiently than long ones, and our data support this view. Our laboratory has shown that aerosolized chrysotile fibers longer than 16 microns can be deposited in the peripheral lung parenchyma of rats, and the measured clearance rate of these fibers is not significantly different from zero. Chrysotile, but no amphibole, fibers split longitudinally, so that the number of retained chrysotile fibers > or = 16 microns in length increases over time. We have not observed significant changes in chemical composition of chrysotile fibers up to 30 days post-deposition in the rat. Nor have we observed translocation of chrysotile fibers from the "central" regions of the lung toward the subpleural regions. However, 1 month after a single 3-hr exposure to chrysotile asbestos, the longest, most pathogenic fibers persist throughout the lung parenchyma. These retained fibers have the potential to cause disease in both parenchyma and pleura.

ZD1542, a potent thromboxane A2 synthase inhibitor and receptor antagonist in vitro.

1. The thromboxane A2 synthase (TXS) inhibitory activity and the thromboxane A2 (TP)-receptor blocking action of ZD1542 (4(Z)-6-[2S,4S,5R)-2-[1-methyl-1-(2-nitro-4-tolyloxy)ethyl]-4-(3- pyridyl)-1,3-dioxan-5-yl]hex-4-enoic acid) has been evaluated in vitro on platelets and whole blood from a range of species including man. Antagonist activity has also been investigated in vascular and pulmonary smooth muscle preparations in vitro. 2. ZD1542 caused concentration-dependent inhibition of human platelet microsomal thromboxane B2 (TXB2) production in vitro (IC50 = 0.016 microM); this inhibition was associated with an increase in prostaglandin E2 (PGE2) and PGF2 alpha formation. 3. ZD1542 also inhibited collagen-stimulated TXS in human, rat and dog whole blood giving IC50 values of 0.018, 0.009 and 0.049 microM respectively. The drug did not modify platelet cyclo-oxygenase activity as inhibition of TXB2 formation was associated with a concomitant increase in the levels of PGD2, PGE2 and PGF2 alpha. ZD1542 had little if any effect against cultured human umbilical vein endothelial cell (HUVEC) cyclo-oxygenase (IC50 > 100 microM) and prostacyclin (PGI2) synthase (IC50 = 18.0 +/- 8.6 microM). 4. ZD1542 caused concentration-dependent inhibition of U46619-induced aggregation responses of human, rat and dog platelets yielding apparent pA2 values of 8.3, 8.5 and 9.1 respectively. The drug was selective as, at concentrations up to 100 microM, it did not modify 5-hydroxytryptamine (5-HT) or the primary phases of adenosine diphosphate (ADP) and adrenaline-induced aggregation. Furthermore, ZD1542 (100 microM) modified only weakly the platelet effects of PGD2, PGE1 and PGI2. 5. ZD1542 also caused concentration-dependent inhibition of U46619-mediated contractions of rat thoracic aorta, guinea-pig trachea and lung parenchyma preparations giving apparent pA2 values of 8.6,8.3 and 8.5 respectively. At concentrations approaching three orders of magnitude greater than those required to block U46619-mediated contractions, the drug did not affect the actions of non-prostanoid agonists or exhibit agonist activity in any of the smooth muscle preparations employed; neither did it interact at EP- or FP-receptors.6. In conclusion, the present study demonstrates that ZD1542 is a drug that exhibits both potent,selective TXS inhibition and TXA2 receptor antagonism.

Heterogeneity in the immunolocalization of cytokeratin-specific monoclonal antibodies in the rat lung: evaluation of three different alveolar epithelial cell types.

The distribution of individual cytokeratin polypeptides in the adult rat lung parenchyma was investigated by immunohistochemistry with 44 monoclonal and 2 polyclonal antibodies. Simple epithelial cytokeratins 7, 8, 18 and 19 were found to be expressed differently in alveolar and bronchial epithelial cells. Three distinct types of alveolar cells were detected according to their pattern of immunoreactivity: type II cells strongly expressing cytokeratins 8 and 18 and weakly expressing cytokeratins 7 and 19 in the cell periphery; type I cells predominantly positive for cytokeratins 7 and 19 and weakly for cytokeratin 8; and a newly defined third cell type III (alveolar brush cell) with cytokeratin 18 abundantly expressed but organized in an unusual intracellular ("globular") structure. The latter cell type failed to bind the type II specific Maclura pomifera lectin, and contained no surfactant proteins. Bronchial epithelial cells exhibited a more or less uniform staining pattern for cytokeratins 8, 18 and 19 and focally for cytokeratins 4 and 7.

A morphometric quantitation of developmental changes in elastic fibers in rat lung parenchyma: variability with lung region and postnatal age.

Elastin has long been thought to play a pivotal role in alveolar septal development by providing the structural framework around which new alveoli develop in the immature lung. This theory was derived from observations that the dramatic increase in lung elastin and alveolar septal development occurred during the same time period, days 4 to 13 in the rat. Using stereologic techniques, we evaluated volume density of respiratory tissue in parenchyma and total length of parenchymal elastic fibers in the lungs of neonatal rats ranging in age from 4 to 26 days. Lung tissue was obtained from each of the four right lung lobes and from the upper, middle, and lower regions of the left lung. When changes in these two parameters in the lung as a whole were considered by averaging values for each of the seven regions, a continuous increase was observed in both the volume of parenchymal tissue in parenchyma and the total length of elastic fibers from days 4 to 22. A significant correlation was found between the volume of respiratory tissue in parenchyma and the length of parenchymal elastic fibers from days 4 to 26, supporting the existing theory that a causal relationship exists between these two parameters. A comparison of the ratios of elastic fiber length to volume density of respiratory tissue in parenchyma (Lv/Vrp) from each of the seven lung regions sampled indicated a significant variability in Lv/Vrp within different regions of the same lung. In addition, the effects of postnatal age and lung region on Lv/Vrp were interdependent; the lung regions that differed with respect to the length density of elastic fibers varied with postnatal age.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue Specificity of Endothelin Binding Sites

A measurement was made of the binding of 125I-labeled endothelin (125I-ET) to crude membrane fractions prepared from rat aorta, atrium, ventricle, portal vein, trachea, lung parenchyma, vas deferens, ileum, bladder, and guinea-pig taenia coli and lung parenchyma. Scatchard analysis of 125I-ET binding in all tissues indicated binding to a single class of saturable sites. The affinity and density of 125I-ET binding sites varied between tissues. The Kd of 125I-ET binding was approximately 0.5 nM for rat aorta, trachea, lung parenchyma, ventricle, bladder, and vas deferens, and guinea-pig taenia coli and lung parenchyma, 1.8 nM for rat portal vein and atrium, and 3.3 nM for ileum. The Bmax of 125I-ET binding had the following rank order of density in rat tissues: trachea greater than lung parenchyma = vas deferens much greater than aorta = portal vein = atrium greater than bladder greater than ventricle = ileum. The properties of 125I-ET endothelin binding were characterized in rat ventricular membranes. 125I-ET binding was time dependent, reaching a maximum within 45-60 min at 25 degrees C. The calculated microassociation constant was 9.67 x 10(5) s-1 M-1. Only 15-20% of 125I-ET dissociated from its binding site even when dissociation was studied as long as 3 h. Preincubation of ventricular membranes with ET prevented binding of 125I-ET. 125I-ET binding was destroyed by boiling of ventricular membranes and was temperature, pH, and cation (Ca2+, Mg2+, and Na+) dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel mechanism of capillary growth in the rat pulmonary microcirculation

Postnatally, the rat lung parenchyma undergoes impressive growth. Within four months of birth, lung volume and alveolar and capillary surface areas increase over 20-fold and capillary volume 35-fold. Investigation of methacrylate casts of the pulmonary microvasculature revealed that, with age, lung capillaries were not only growing in surface and volume but also increasing their network density. We proposed that the capillary bed grows by formation of slender intravascular tissue pillars and termed this type of growth intussusceptive microvascular growth (Caduff et al., Anat. Rec., 216:154-164, 1986). The aim of this investigation was to detect the presence and to analyze the ultrastructure of slender tissue posts (diameter 1-2.5 microns) extending across the capillary lumina in serial electron microscopic sections of rat lung parenchyma (age 44 days). Computer-assisted three-dimensional reconstruction of the capillary lumen confirmed that tissue posts were matching the holes previously observed in casts. Post ultrastructure varied with size from a simple area of interendothelial contact to tissue pillars with a core of interstitial tissue. Based on the changing morphology of the pillars, a hypothesis for their development can be proposed: phase I, creation of a zone of contact between opposite capillary walls (formation of an interendothelial bridge); phase II, reorganization of the intercellular junctions of the endothelium, with central perforation of the capillary layer; phase III, formation of an interstitial post core, with successive invasion by cytoplasmic extensions of myofibroblasts, pericytes, and finally interstitial fibers; and phase IV, growth of the slender pillar to a normal full size capillary mesh. These findings support the new concept of intussusceptive growth of the lung capillary system.

High-affinity binding of mequitamium iodide (LG 30435) to muscarinic and histamine H 1 receptors

Mequitamium iodide (LG 30435) is a novel quaternary ammonium phenothiazine with potential as an anti-asthmatic agent. In vitro binding experiments were performed in order to clarify the molecular mechanisms underlying its biological activity. Mequitamium iodide was found to bind with high affinity only to histamine H 1 receptors in rat brain membranes (K i = 9 nM) and to muscarinic acetylcholine receptors in various tissues homogenates (K i = 12–77 nM) with no clearcut selectivity for any of the known subtypes. The interaction with muscarinic receptors in rat cerebral cortex and lung parenchyma was competitive, as showed by saturation studies. Lower affinity values (K i = 1–10 μM) were found for serotonin 5-HT 2, platelet-activating factor (PAF), verapamil and β-adrenergic agents. These results indicate that both the potent antimuscarinic and antihistamine and the relatively weak anti-PAF pharmacological effects of mequitamium iodide may be explained by the direct interaction of the substance with the respective receptors.

Health effects of acid aerosols formed by atmospheric mixtures.

Under ambient conditions, sulfur and nitrogen oxides can react with photochemical products and airborne particles to form acidic vapors and aerosols. Inhalation toxicological studies were conducted, exposing laboratory animals, at rest and during exercise, to multicomponent atmospheric mixtures under conditions favorable to the formation of acidic reaction products. Effects of acid and ozone mixtures on early and late clearance of insoluble radioactive particles in the lungs of rats appeared to be dominated by the oxidant component (i.e., the mixture did cause effects that were significantly different from those of ozone alone). Histopathological evaluations showed that sulfuric acid particles alone did not cause inflammatory responses in centriacinar units of rat lung parenchyma (expressed in terms of percent lesion area) but did cause significant damage (cell killing followed by a wave of cell replication) in nasal respiratory epithelium, as measured by uptake of tritiated thymidine in the DNA of replicating cells. Mixtures of ozone and nitrogen dioxide, which form nitric acid, caused significant inflammatory responses in lung parenchyma (in excess of effects seen in rats exposed to ozone alone), but did not damage nasal epithelium. Mixtures containing acidic sulfate particles, ozone, and nitrogen dioxide damaged both lung parenchyma and nasal epithelia. In rats exposed at rest, the response of the lung appeared to be dominated by the oxidant gas-phase components, while responses in the nose were dominated by the acidic particles. In rats exposed at exercise, however, mixtures of ozone and sulfuric acid particles significantly (2.5-fold) elevated the degree of lung lesion formation over that seen in rats exposed to ozone alone under an identical exercise protocol.

Lack of turnover of inositol phosphates in guinea-pig and rat lung parenchyma may be due to its dependence on extracellular calcium during contraction

Lack of turnover of inositol phosphates in guinea-pig and rat lung parenchyma may be due to its dependence on extracellular calcium during contraction

Asbestos‐induced changes in rat lung parenchyma

Fischer 344 rats have been exposed to UICC crocidolite by whole-body inhalation procedures for periods of 1 d to 12 mo. Material was obtained from the same location in the left lung, and the numbers of cells in the parenchyma were identified and determined by transmission electron microscopy. An immediate increase (1 d of exposure) was evident in the number of type II cells, suggesting a direct action of the dust on these cells. The number of interstitial and alveolar macrophages showed a significant increase after 3 mo of exposure. The number of alveolar macrophages containing dust particles after a 1-d exposure was 49%, and the corresponding value after 12 mo of exposure was 92%. The longer periods of exposure were associated with an increase in the number of particles per macrophage. Polymorphs appeared in the interstitium at airway bifurcations, prior to their appearance in the alveolar space. These bifurcations were also the initial sites where evidence of cell damage and collagen deposition was seen. In this experiment crocidolite appears to be weakly fibrogenic, and other factors may be needed to produce the marked lesions seen in human asbestosis.

Lung tissue tension and glycosaminoglycans

This study tested the hypothesis that the loss of tissue tension which occurs when lung parenchyma is immersed in phosphate buffered saline (PBS) follows a loss of glycosaminoglycans (GAG) and/or protein. Tissue tension decay (TTD) was examined in 30 × 30 × 100 μm strips of rat lung parenchyma immersed in PBS in the presence of agents altering the loss of GAG. GAG were labeled with [35S]sulfate in vitro by tissue culture of lung explants and in vitro by intraperitoneal injection of [35S]sulfate. Labeled GAG were lost from lung explants, lung homogenates, and whole lung immersed in saline. The rate of GAG loss was found to correlate with early TTD. In the presence of agents that markedly reduced the leach rate of GAG from lung parenchyma (Safranin O, Alcian Blue, Acridine Orange) there was no TTD. Cetyl-pyridinium chloride was also effective. Polybrene, however, caused a significantly greater TTD than seen in saline with some reduction in the total amount of GAG leached from the tissue. Greater amounts of heparin sulfate were lost in the presence of polybrene. Human serum, dextran-70, ovalbumin, and gelatin significantly reduced but did not prevent TTD. Dextran-70 was effective in reducing the loss of GAG from tissue explants. Agents that reduced disulfide bonds (dithiothreitol, 2-mercaptoethanol) markedly increased TTD and increased the loss of GAG and protein from lung explants and lung homogenates. These studies provide further evidence that lung tissue tension is a function of the interstitial matrix interacting with the connective tissue network. When the GAG and protein responsible for the swelling pressure of matrix are preserved the tissue tension is stable for one hour or more. Agents that partially preserve the matrix are somewhat effective in reducing TTD while those that increase the loss of GAG and protein increase the loss of tension. From the differential effect of agents that retard and accelerate GAG, heparin sulfate (HS) may be the most important GAG to the tissue properties.

Arachidonic acid metabolites induced β-adrenoceptor densitization in rat lung in vitro

The possible involvement of arachidonic acid (AA) or its metabolites in β-adrenoceptor desensitization has been studied in rat lung parenchyma both from a functional and a biochemical point of view. In vitro perfusion of rat lungs with AA (3×10 −5M for 20 min) reduced the relaxant effect of isoproterenol (ISO) on lung parenchymal strips, shown by a shift to the right of ISO dose-response curve, similar to that obtained using desensitizing concentration of specific β-agonist. Moreover, AA treatment reduced the capacity of ISO to stimulate adenylate-cyclase activity, whereas the number of β-receptor binding sites was not significantly modified. Inhibition of cyclo-oxygenase pathway by indomethacin (INDO) (1.5 × 10 −5M) prevented both the loss of ISO-relaxing capacity and the decrease of adenylate-cyclase activity induced by AA treatment. In order to support the role of eicosanoids in β-adrenoceptor desensitization, changes of endogenous free AA levels have also been studied in lung homogenates. Perfusion of rat lung with ISO (10 −6M for 20 min) decreased by about 50% the levels of free AA and the pretreatment with BW755C (9×10 −5M), a lipo- and cyclo-oxygenase inhibitor, prevented this phenomenon. On the basis of these results, we suggest that the activation of AA cascade is actually involved in β-adrenoceptor desensitization in lung tissues with a possible interference at the site beyond the drug-receptor interaction.

Involvement of arachidonic acid metabolites in β-adrenoceptor desensitization: Functional and biochemical studies

The prolonged in vitro perfusion of rat lung with isoproterenol (Iso) induced a desensitization of β-adrenoceptors which was dose- and time-dependent. The decrease in functional responsiveness of rat lung parenchyma to the β-agonist correlated well with the loss of [ 3H]dihydroalprenolol ([ 3H]DHA) binding sites and adenylate cyclase activity after the β-adrenoceptor desensitization procedure. The cyclooxygenase inhibitor indomethacin prevented the β-adrenoceptor desensitization as was shown by the restored isoproterenol-induced relaxation in rat lung parenchyma strips and adenylate cyclase activity after the milder desensitization procedure. Inhibition of the arachidonic acid cascade at different levels with different compounds such as BW 755C and betamethasone prevented the desensitization of β-adrenoceptors. These findings suggest a role for arachidonic acid metabolites in β-adrenoceptor desensitization. The possible sites of action of arachidonic acid metabolites are also discussed in relation to the inability of indomethacin to prevent the desensitization of β-adrenoceptors that was induced by the higher Iso concentration used.

Separation and Characterization of Lymphocytes from Rat Lung Parenchyma

Rat pulmonary parenchymal tissue was disaggregated into a single cell suspension by treatment with collagenase. A cell population enriched for lung lymphocytes was separated by depletion of adherent cells on a Sephadex G-10 column: 16.7 +/- 2.7 X 10(6) cells per animal were recovered. On the basis of cytochemical and morphologic criteria, the separated cells contained greater than 80% lymphocytes, with a viability of 80-90%. The distribution of lymphocyte subpopulations was determined by indirect immunoperoxidase staining with appropriate monoclonal antibodies. Separated lung lymphocytes exhibited a proliferative response in vitro to phytohemagglutinin and concanavalin A. Supernatants from lung lymphocytes stimulated with concanavalin A contained lymphokine activity that could be demonstrated in a leukocyte procoagulant activity assay.

Ultrastructural analysis of changes in the lung parenchyma in the initial stage of experimental sepsis

Histological and ultrastructural alterations in the lung parenchyma of rats with sepsis induced by implantation of 3 X 10(10) microorganisms (P. aeruginosa) beneath the skin were studied. Microorganisms with micropili were detected in septal spaces and in the alveoli 10 hours after implantation. Their effects were linked with microcirculatory alterations and destruction of endotheliocytes, alveolocytes and septal cells.

Source of lung surfactant phospholipids: comparison of palmitate and acetate as precursors.

The phospholipids and the fatty acid compositions of major phospholipids in rat lung parenchyma, microsomes, lamellar bodies and alveolar wash were quantified. Adult rats were injected simultaneously with [3H]palmitate and [14C]acetate into the femoral vein. The appearance of labeled phosphatidylcholine (PC), desaturated phosphatidylcholine (DSPC) and phosphatidylglycerol (PG) in each lung fraction was measured during short periods of time (5 min to 2 hr) after isotope administration. Relatively more PC, DSPC and PG labeled with acetate radioactivity in lung microsomes entered lamellar body and alveolar wash fractions than those labeled with palmitate radioactivity. However, there was no difference between palmitate and acetate labeled phospholipids in the transport from microsomes to lamellar bodies by phospholipid exchange proteins. On the other hand, prior injection of colchicine resulted in decrease in the transport of PC from microsomes to alveolar space to a relatively greater extent in the acetate radioactivity than in the palmitate radioactivity.

Characteristics of a clone of endothelial cells derived from a line of normal adult rat lung cells.

A strain of endothelial cells derived from a single cell cloned from a line of normal adult rat lung parenchyma has been maintained in tissue culture for more than 3 years. These cells have been identified as endothelial cells based on the combination of their growth characteristics, cell morphology as observed with both light and electron microscopy, and their physiological properties. They have continued to produce granules, which stain specifically for glycosaminoglycans with Alcian blue, for over 2 1/2 years. During the same period of time, glycosaminoglycans were identified biochemically in both cells and medium. They have maintained the ability to degrade bradykinin over this period as well.