Biomedical subjects

D M McDonald

Publications and source records attributed to D M McDonald.

At least 37 records · Page 2Linked to original sources

PubMed1999

Distribution of adjuvant MF59 and antigen gD2 after intramuscular injection in mice.

MF59, which is an adjuvant approved for human use, typically elicits higher antibody titers than alum when used in combination with a variety of recombinant and natural subunit antigens. The mechanisms responsible for the adjuvant action of MF59 are not fully understood. In particular, little is known about the in vivo distribution of MF59 and of antigen after intramuscular (i.m.) injection. The goal of the present study was to determine the distribution of MF59 injected with soluble antigen gD2 from type 2 herpes simplex virus (HSV) and to compare the distribution of gD2 injected with or without MF59. At 4 h, 36% of the injected dose of labeled MF59 was in the quadriceps muscle and about 50% was in the inguinal fat surrounding the muscle. Half of the initial amount of labeled MF59 in muscle was detected 42 h after injection. The amount of labeled MF59 in the draining lymph nodes was maximal 2 d after injection, which represented 0.1-0.3% of the injected dose. At 4 h, 12% of the injected dose of labeled gD2 was found in the muscle. The presence of MF59 did not significantly modify the distribution of gD2. The results indicate that MF59 and gD2 distribute and are cleared independently after i.m. injection. Importantly, MF59 is unlikely to have a repository effect, whereby it slowly releases the antigen.

Adjuvants, Immunologic↗

PubMed1999

Vascular endothelial-cadherin is an important determinant of microvascular integrity in vivo.

In the present paper, we characterize an antibody, mAb BV13, directed to mouse vascular endothelial (VE)-cadherin, a major adhesive protein of interendothelial adherens junctions. When added to cultured endothelial cells, BV13 induces a redistribution of VE-cadherin from intercellular junctions. VE-cadherin redistribution did not change the localization of platelet endothelial cell adhesion molecule or tight junction markers such as zonula occludens 1, cingulin, and junctional adhesion molecule. Intravenous administration of mAb BV13 induced a concentration- and time-dependent increase in vascular permeability in heart and lungs. By electron microscopy, interstitial edema and accumulation of mixed types of inflammatory cells in heart and lungs were observed. Injection of (rhodamine-labeled) Ricinus communis I lectin showed focal spots of exposed basement membrane in the alveolar capillaries and in some larger pulmonary vessels. These data indicate that VE-cadherin is required for vascular integrity and normal organ functions.

Animals↗

PubMed1999

Endothelial cell heterogeneity in venules of mouse airways induced by polarized inflammatory stimulus.

We sought to determine whether the changes in microvascular endothelial cells (EC) caused by a polarized chronic inflammatory stimulus depend on proximity to the stimulus. C3H mice were infected with Mycoplasma pulmonis, which attaches to the airway epithelium and creates a polarized inflammatory stimulus across the airway wall. At 1, 2, or 4 weeks, the tracheal vasculature was stained by perfusion of silver nitrate to mark EC borders or biotinylated Lycopersicon esculentum lectin to label the EC surface and adherent leukocytes. E-selectin immunoreactivity and EC proliferation were also localized. We found that the size, shape, and immunoreactivity for adhesion molecules on EC nearest the airway lumen (subepithelial EC) were different from those on the opposite surface of the same vessels. Subepithelial EC were smaller, more irregular in shape, had greater E-selectin immunoreactivity, and had twice as many adherent leukocytes. In contrast, proliferating EC were uniformly distributed around the vessel circumference. We conclude that the polarized stimulus created by M. pulmonis infection differentially changes the size, shape, and function of EC nearest the airway epithelium. This heterogeneity may result from a gradient of inflammatory mediators that triggers the influx of leukocytes into the airway lumen.

Animals↗

PubMed1999

Neurogenic plasma leakage in mouse airways.

1. This study sought to determine whether neurogenic inflammation occurs in the airways by examining the effects of capsaicin or substance P on microvascular plasma leakage in the trachea and lungs of male pathogen-free C57BL/6 mice. 2. Single bolus intravenous injections of capsaicin (0.5 and 1 micromol kg(-1), i.v.) or substance P (1, 10 and 37 nmol kg(-10, i.v.) failed to induce significant leakage in the trachea, assessed as extravasation of Evans blue dye, but did induce leakage in the urinary bladder and skin. 3. Pretreatment with captopril (2.5 mg kg(-1), i.v.), a selective inhibitor of angiotensin converting enzyme (ACE), either alone or in combination with phosphoramidon (2.5 mg kg(-1), i.v.), a selective inhibitor of neutral endopeptidase (NEP), increased baseline leakage of Evans blue in the absence of any exogenous inflammatory mediator. The increase was reversed by the bradykinin B2 receptor antagonist Hoe 140 (0.1 mg kg(-1), i.v.). 4. After pretreatment with phosphoramidon and captopril, capsaicin increased the Evans blue leakage above the baseline in the trachea, but not in the lung. This increase was reversed by the tachykinin (NK1) receptor antagonist SR 140333 (0.7 mg kg(-1), i.v.), but not by the NK2 receptor antagonist SR 48968 (1 mg kg(-1), i.v.). 5. Experiments using Monastral blue pigment as a tracer localized the leakage to postcapillary venules in the trachea and intrapulmonary bronchi, although the labelled vessels were less numerous in mice than in comparably treated rats. Blood vessels of the pulmonary circulation were not labelled. 6. We conclude that neurogenic inflammation can occur in airways of pathogen-free mice, but only after the inhibition of enzymes that normally degrade inflammatory peptides. Neurogenic inflammation does not involve the pulmonary microvasculature.

Adrenergic beta-Antagonists↗

PubMed1999

Tissue macrophages associated with angiogenesis in chronic airway inflammation in rats.

Angiogenesis is a feature of chronic inflammation produced by Mycoplasma pulmonis infection of the respiratory tract. The mechanism of this angiogenesis is unknown, but cellular growth factors and matrix remodeling proteases produced by inflammatory cells are likely to be involved. The goal of this study was to determine the relationship between changes in the number, shape, and distribution of ED2-immunoreactive macrophages and the development of angiogenesis in the tracheal mucosa of Wistar rats after M. pulmonis infection. In pathogen-free rats, ED2-positive cells were scattered in the airway mucosa (261 +/- 42 cells/mm2 of surface, mean +/- SE). Most cells were irregularly shaped and had moderate ED2 immunoreactivity. No lymphoid tissue was present. The number of ED2-positive cells increased rapidly after infection, was 120% above baseline at 1 wk, and remained significantly increased throughout the 4-wk study (P < 0.05). Angiogenesis was first detected at 2 wk, and at 3 wk the vessel length density was nearly 8-fold the pathogen-free value. At 3 and 4 wk, focal sites of angiogenesis coincided with discrete clusters of round, strongly immunoreactive ED2-positive cells (1,340 +/- 124 cells/mm2) in polyp-like collections of mucosal lymphoid tissue. The close association of distinctive ED2-positive cells with angiogenic blood vessels suggests a relationship between a subset of tissue macrophages and the angiogenesis associated with M. pulmonis infection. The time course of the changes indicates that the initial influx of ED2-positive macrophages precedes the angiogenesis, and the rounding of the cells parallels the growth of new vessels.

Animals↗

PubMed1999

Endothelial gaps as sites for plasma leakage in inflammation.

OBJECTIVE: In 1961, Majno and Palade proposed that plasma leakage in acute inflammation caused by histamine, serotonin, or bradykinin results via gaps that form between endothelial cells of postcapillary venules. Now the relevance of endothelial gaps in plasma leakage is being questioned. The purpose of this review is to summarize experimental evidence from our studies showing that endothelial gaps participate in plasma leakage in inflammation. METHODS: Using neurogenic inflammation as a model of plasma leakage in acute inflammation, we compared five methods to determine whether endothelial gaps form in the microvasculature of the rat trachea. 1) Endothelial cells borders and gaps were stained with silver nitrate and visualized by light, scanning, and transmission electron microscopy. 2) The luminal surface of endothelial cells was examined by scanning electron microscopy. 3) The luminal surface of endothelial cells was stained with a biotinylated lectin and avidin-biotin-peroxidase histochemistry, and then was examined by differential interference contrast microscopy. 4) Endothelial junctions were reconstructed from serial sections photographed by transmission electron microscopy. 5) Leakage was measured after perfusion of lectins or tracers through aldehyde-fixed vessels in situ. RESULTS: The results from the five methods used in this system were consistent with the formation of gaps between endothelial cells. Endothelial gaps were rare or absent under baseline conditions, but appeared with the onset of plasma leakage and had a distribution that matched the distribution of leakage. Gaps had a complex morphology and were accompanied by fingerlike cell processes, which may anchor adjacent endothelial cells to one another and participate in gap closure. In contrast to normal vessels, vessels that were leaky in life continued to leak after aldehyde fixation, in evidence that, once formed, the leakage pathway did not require energy-dependent membrane movement or vesicle shuttling. Holes through endothelial cells were less than 1% as frequent as intercellular gaps. CONCLUSIONS: Taken together, the results show that endothelial gaps are a consistent feature of leaky vessels in the model system we studied, and are not an artifact of a particular method. The morphological complexity of the openings and accompanying fingerlike cell processes and overlapping endothelial cell borders make gaps difficult to distinguish from transcellular holes in thin sections viewed by transmission electron microscopy. However, scanning electron microscopic observations show that most of the openings in leaky venules are intercellular gaps, not transcellular holes. The formation and closure of gaps are likely to be energy-dependent, but the process of plasma leakage is not, provided there is adequate driving force for extravasation. The cellular mechanisms of gap opening and closure remain to be elucidated.

Animals↗

PubMed1998

Increased vascularization in mice overexpressing angiopoietin-1.

The angiopoietins and members of the vascular endothelial growth factor (VEGF) family are the only growth factors thought to be largely specific for vascular endothelial cells. Targeted gene inactivation studies in mice have shown that VEGF is necessary for the early stages of vascular development and that angiopoietin-1 is required for the later stages of vascular remodeling. Here it is shown that transgenic overexpression of angiopoietin-1 in the skin of mice produces larger, more numerous, and more highly branched vessels. These results raise the possibility that angiopoietins can be used, alone or in combination with VEGF, to promote therapeutic angiogenesis.

Angiopoietin-1↗

PubMed1998

Dendritic cells internalize vaccine adjuvant after intramuscular injection.

Vaccine adjuvants help antigens elicit rapid, potent, and long-lasting immune responses. The lack of understanding of the immunological mechanism of action of adjuvants has limited the rational development of vaccines for human use. In particular, little is known about how the immune system processes adjuvants. The goal of the present study was to determine the fate of the vaccine adjuvant MF59, labeled with the fluorescent dye Dil, after injection with fluorescein-labeled gD2 antigen from type 2 herpes simplex virus. At 3 h after intramuscular injection into BALB/c mice, most of the MF59 was still in the form of extracellular droplets in the muscle, but a detectable fraction of the MF59 was in cells in the subcapsular sinus of draining inguinal lymph nodes. At 48 h, most of the MF59 at the site of injection was inside cells that were immunoreactive for the dendritic cell markers DEC-205 and MHC class II molecules, reflecting the interaction of MF59 with antigen presenting cells. At this time, intracellular MF59 was also abundant in the paracortical (T cell) region of lymph nodes. The gD2 antigen was also intracellular in muscle and colocalized MF59 at 48 h, and the presence of MF59 increased the amount of intracellular antigen. Similarly, serological antibody titers to gD2 were 207-fold higher after two injections when MF59 was administered with the antigen. These findings suggest that MF59 interacts with antigen presenting cells at the site of injection and then moves to the draining lymph nodes, where it increases the efficiency of antigen presentation to T cells.

Adjuvants, Immunologic↗

PubMed1998

Cationic liposomes target angiogenic endothelial cells in tumors and chronic inflammation in mice.

This study sought to determine whether angiogenic blood vessels in disease models preferentially bind and internalize cationic liposomes injected intravenously. Angiogenesis was examined in pancreatic islet cell tumors of RIP-Tag2 transgenic mice and chronic airway inflammation in Mycoplasma pulmonis-infected C3H/HeNCr mice. For comparison, physiological angiogenesis was examined in normal mouse ovaries. We found that endothelial cells in all models avidly bound and internalized fluorescently labeled cationic liposomes (1,2-dioleoyl-3-trimethylammonium-propane [DOTAP]/cholesterol or dimethyldioctadecyl ammonium bromide [DDAB]/cholesterol) or liposome-DNA complexes. Confocal microscopic measurements showed that angiogenic endothelial cells averaged 15-33-fold more uptake than corresponding normal endothelial cells. Cationic liposome-DNA complexes were also avidly taken up, but anionic, neutral, or sterically stabilized neutral liposomes were not. Electron microscopic analysis showed that 32% of gold-labeled liposomes associated with tumor endothelial cells were adherent to the luminal surface, 53% were internalized into endosomes and multivesicular bodies, and 15% were extravascular 20 min after injection. Our findings indicate that angiogenic endothelial cells in these models avidly bind and internalize cationic liposomes and liposome-DNA complexes but not other types of liposomes. This preferential uptake raises the possibility of using cationic liposomes to target diagnostic or therapeutic agents selectively to angiogenic blood vessels in tumors and sites of chronic inflammation.

Animals↗

PubMed1998

Angiogenesis in mice with chronic airway inflammation: strain-dependent differences.

Chronic inflammation is associated with blood vessel proliferation and enlargement and changes in vessel phenotype. We sought to determine whether these changes represent different types of angiogenesis and whether they are stimulus dependent. Chronic airway inflammation, produced by infection with Mycoplasma pulmonis, was compared in strains of mice known to be resistant (C57BL/6) or susceptible (C3H). Tracheal vascularity, assessed in whole mounts after Lycopersicon esculentum lectin staining, increased in both strains at 1, 2, 4, and 8 weeks after infection, but the type of vascular remodeling was different. The number of vessels doubled in tracheas of C57BL/6 mice, with corresponding increases of capillaries and venules. In contrast, neither the number nor the length of vessels changed in C3H mice. Instead, vessel diameter and endothelial cell number doubled, and the proportion of venules doubled with a corresponding decrease of capillaries. Although the infection had no effect on baseline plasma leakage, in both strains it potentiated the leakage produced by substance P. We conclude that the same stimulus can result in blood vessel proliferation or enlargement, depending on the host response. Endothelial cells proliferate in both cases, but in one case new capillaries form whereas in the other capillaries convert to venules.

Animals↗

PubMed1998

Prevalence, incidence, and clinical characteristics of hepatitis G virus/GB virus C infection in Scottish blood donors.

The prevalence, incidence, clinical features, and natural history of hepatitis G virus (HGV) or GB virus C (GBV-C) were investigated in a non-remunerated blood donor population to determine its clinical significance and its impact on blood safety. Of 1020 regular blood donors, 23 (2.25%) were positive for plasma HGV/GBV-C RNA. Alanine aminotransferase levels were lower than in uninfected donors (median, 20 IU/mL; 32 IU/mL in controls; P=.015). Clinical examination produced no other evidence for hepatitis or for shared nonhepatic diseases. Fifteen of 17 donors excreted HGV/GBV-C in saliva (mean level, 8x103 copies of RNA/mL). Testing of previous donations indicated an incidence of 170-200 new infections with HGV/GBV-C per 100,000 donor-years. The absence of further clinicopathologic data and the limitations of current polymerase chain reaction-based methods for screening suggests that it is neither necessary nor practical to commence screening.

Adult↗

PubMed1998

Glucocorticoid-induced apoptosis of dendritic cells in the rat tracheal mucosa.

Dendritic cells are antigen-presenting cells that constitutively express high levels of major histocompatibility complex class II (Ia) antigen on their plasma membrane. Previous studies have shown that the number of dendritic cells in the rat airway mucosa decreases rapidly after glucocorticoid treatment. We sought to determine whether apoptosis contributes to this steroid-induced cell decrease. Dendritic cells in tracheal whole mounts were revealed by immunoperoxidase staining using the OX-6 (anti-Ia) monoclonal antibody. In untreated rats, a dense network of Ia-immunoreactive (Ia+) cells with highly branched cytoplasmic processes was observed just beneath the tracheal epithelium (1,405 +/- 140 cells/mm2 mucosa; mean +/- SEM, n = 6). In rats treated with dexamethasone (10 mg/kg, intraperitoneally), four distinct changes in dendritic cell morphology were evident 4 to 8 h after injection: (1) appearance of large Ia+ granules in cytoplasmic processes, (2) narrowing of cytoplasmic processes, (3) loss of Ia immunoreactivity from the cell surface, and (4) fragmentation of cells into small Ia+ bodies. These changes accompanied a 56% decrease in the number of Ia+ cells over 8 h. The contribution of apoptosis to this decrease in Ia+ cells was determined by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) of nucleosomal DNA fragments in histologic sections. The number of TUNEL+ bodies increased from a control value of 174 +/- 47 bodies/mm2 mucosa to 2,108 +/- 294 bodies/mm2 mucosa at 4 h and 936 +/- 343 bodies/ mm2 mucosa at 8 h (n = 4 rats per time point). The location of TUNEL+ bodies closely corresponded to that of Ia+ cells stained in adjacent histologic sections. We conclude that apoptosis contributes to the rapid decrease in airway dendritic cells after glucocorticoid treatment.

Animals↗

PubMed1998

Endothelial gaps and adherent leukocytes in allergen-induced early- and late-phase plasma leakage in rat airways.

Exposure of sensitized individuals to antigen can induce allergic responses in the respiratory tract, manifested by early and late phases of vasodilatation, plasma leakage, leukocyte influx, and bronchoconstriction. Similar responses can occur in the skin, eye, and gastrointestinal tract. The early-phase response involves mast cell mediators and the late-phase response is leukocyte dependent, but the mechanism of leakage is not understood. We sought to identify the leaky blood vessels, to determine whether these vessels contained endothelial gaps, and to analyze the relationship of the gaps to adherent leukocytes, using biotinylated lectins or silver nitrate to stain the cells in situ and Monastral blue as a tracer to quantify plasma leakage. Most of the leakage occurred in postcapillary venules (< 40-microns diameter), whereas most of the leukocyte migration (predominantly neutrophils) occurred in collecting venules. Capillaries and arterioles did not leak. Endothelial gaps were found in the leaky venules, both by silver nitrate staining and by scanning electron microscopy, and 94% of the gaps were distinct from sites of leukocyte adhesion or migration. We conclude that endothelial gaps contribute to both early and late phases of plasma leakage induced by antigen, but most leakage occurs upstream to sites of leukocyte adhesion.

Allergens↗

PubMed1997

Characterization of tolerance to the anti-leakage effect of formoterol in rat airways.

These experiments addressed the question of whether the anti-plasma leakage action of beta2-adrenoceptor agonists in rat airways is subject to tolerance. Pathogen-free F344 rats were pretreated with the highly selective, long-acting beta2-adrenoceptor agonist, formoterol (0, 0.1, 1, 10 microg/kg, i.p.) for 7 days; 24 h later the effectiveness of acute doses of formoterol (0, 0.1, 1, 10 microg/kg, i.v.) was tested against substance P-induced plasma leakage. The anti-leakage effect of formoterol was not subject to tolerance with the low or intermediate pretreatment dose. Pretreatment with 10 microg/kg formoterol reduced the effectiveness of the 1 microg/kg acute dose but not the 10 microg/kg acute dose. We conclude that tolerance to the anti-leakage effect of formoterol can occur, but airway vessels are likely to retain functionally coupled receptors even after high dose pretreatment.

Adrenergic beta-Agonists↗

PubMed1997

Organ-specific endothelial cell uptake of cationic liposome-DNA complexes in mice.

This study identified the organ and cellular distribution of cationic liposome-DNA complexes injected intravenously into CD-1 mice for gene delivery. DOTIM-cholesterol liposomes were labeled with the fluorescent dye CM-Dil and complexed with plasmid DNA encoding the chloramphenicol acetyltransferase reporter gene. The distribution of the complexes was examined in 29 organs and tissues by fluorescence, confocal, and electron microscopy from 5 min to 24 h after injection. The complexes formed clusters in blood, which were cleared within 20 min. Complexes visible by fluorescence microscopy were taken up by endothelial cells, leukocytes, and macrophages and did not leave the vasculature except in the spleen. At 5 min, the complexes formed a patchy coating on the endothelial surface, but by 4 h, they were internalized into endosomes and lysosomes in organ- and vessel-specific patterns. Uptake by capillary endothelial cells was greatest in the lung, ovary, and anterior pituitary, less in muscle and the heart, and nearly absent in the brain and pancreatic islets. In lymph nodes and intestinal Peyer's patches, the uptake was sparse in capillaries but abundant in high endothelial venules. In the liver and spleen, most of the uptake was in Kupffer cells and macrophages. Measurements of chloramphenicol acetyltransferase reporter gene expression were generally consistent with the pattern of uptake by endothelial cells. The uptake and gene expression were accompanied by a decrease in circulating leukocytes and platelets. Overall, our results showed that the complexes were internalized by endothelial cells in organ- and vessel-specific patterns that did not match any previously identified properties of the microvasculature. The unusual distribution of endothelial cell uptake may be explained by a heterogeneously distributed membrane receptor for which the complexes are ligands.

Animals↗

PubMed1997

Endothelial gaps: time course of formation and closure in inflamed venules of rats.

In the rat trachea, substance P causes rapid but transient plasma leakage. We sought to determine how closely the number, morphology, and size of endothelial gaps correspond to the time course of this leakage. Endothelial gaps were examined by scanning electron microscopy (EM), by transmission EM, or by light microscopy after silver nitrate staining. Substance P-induced leakage of the particulate tracer Monastral blue peaked at 1 min but decreased with a half-life of 0.3 min. The number of silver-stained gaps also peaked at 1 min then decreased significantly more slowly (half-life 1.9 min) than the leakage. Scanning EM revealed two types of endothelial gaps, designated vertical gaps and oblique slits. Vertical gaps predominated at peak leakage, whereas oblique slits became more common as the leakage diminished. Measurements of the mean diameter of vertical gaps made by light microscopy, scanning EM, and transmission EM were all in the range of 0.36-0.47 micron. Fingerlike endothelial cell processes that appeared during gap formation became shorter as the leakage diminished (mean length: 1.44 microns at 1 min compared with 1.06 microns at 3 min after substance P), suggesting a role in gap closure. We conclude that the plasma leakage occurring immediately after an inflammatory stimulus results from the rapid formation of endothelial gaps. Multiple factors, including alterations in gap morphology, gap closure, and changes in driving force, are likely to participate in the rapid decrease in the leakage.

Animals↗

PubMed1997

Upregulation of substance P receptors in angiogenesis associated with chronic airway inflammation in rats.

In rat airways, substance P released from sensory nerves induces plasma leakage via neurokinin-1 (NK1) receptors on endothelial cells. In pathogen-free rats, both leakage and endothelial NK1 receptors are most abundant in postcapillary venules. In Mycoplasma pulmonis-infected rats, extensive angiogenesis occurs in the tracheal mucosa. The capillary-sized (< 10 microns in diameter) angiogenic blood vessels are abnormally sensitive to substance P. The aim of this study was to determine whether increased expression of NK1 receptors contributes to this abnormal sensitivity. Fischer 344 rats were infected with M. pulmonis and were challenged with substance P (5 micrograms/kg i.v.), and then plasma leakage in the tracheal mucosa was measured by extravasation of Monastral blue (30 mg/kg i.v.). NK1 receptors on endothelial cells were localized by immunohistochemistry. Five minutes after substance P, NK1 receptor-immunoreactive endosomes were five times more abundant in endothelial cells of angiogenic capillaries in M. pulmonis-infected rats than in corresponding capillaries in pathogen-free controls (17.1 +/- 2.3 vs. 3.5 +/- 0.4 endosomes/100 micron 2 of endothelial surface). Endosomes were slightly more abundant in postcapillary venules 15-35 microns in diameter in infected rats (23.0 +/- 0.6 vs. 19.2 +/- 0.7 endosomes/100 micron 2). Similarly, after substance P, angiogenic capillaries had much more Monastral blue labeling (area density: 18.8 +/- 1.5 vs. 2.9 +/- 0.5% of vessel wall), whereas postcapillary venules had about the same amount of labeling (36.0 +/- 3.7 vs. 34.1 +/- 1.8%). We conclude that increased expression of NK1 receptors, which are internalized into endosomes after ligand binding, contributes to the abnormal sensitivity of endothelial cells of angiogenic blood vessels to substance P in the airways of M. pulmonis-infected rats.

Animals↗

PubMed1997

Salmeterol reduces early- and late-phase plasma leakage and leukocyte adhesion in rat airways.

We examined the effect of salmeterol, a long-acting beta2-adrenergic receptor agonist, on ovalbumin-induced plasma leakage and leukocyte adhesion in tracheal blood vessels of unanesthetized brown Norway rats. Ovalbumin challenge of sensitized rats resulted in both early and late phases of plasma leakage as measured with Evans blue. The early phase occurred during the challenge. The late phase began 2 h after the challenge, peaked at 4 h, and ended by 24 h. Ovalbumin challenge also increased the number of adherent leukocytes in mucosal blood vessels at 4 h. Nebulized salmeterol (5 mg/ml for 10 min) administered before the challenge inhibited the early-phase leak by 26%, 58%, or 85%, depending upon whether the interval between pretreatment and challenge was 0.5, 1, or 4.5 h, respectively. Similarly, salmeterol pretreatment (0.05 to 5 mg/ml for 10 min) reduced the late-phase leak at 4 h. Late-phase leakage was completely blocked at concentrations of 0.5 mg/ml or greater. This inhibitory effect was prevented by prior injection of the beta2-adrenergic receptor antagonist ICI-118,551. Salmeterol pretreatment also reduced the adherence of neutrophils, eosinophils, monocytes, and lymphocytes in mucosal blood vessels at 4 h. We conclude that salmeterol pretreatment can reduce the plasma leakage and leukocyte adhesion in early- and late-phase responses after antigen challenge through its action on beta2 receptors.

Adrenergic beta-2 Receptor Antagonists↗