Airway reactivity, inflammatory cell influx and nitric oxide in guinea-pig airways after lipopolysaccharide inhalation

1. The aim of this study was to investigate the relationship between airway reactivity, leukocyte influx and nitric oxide (NO), in conscious guinea-pigs after aerosolized lipopolysaccharide (LPS) exposure. 2. Inhaled histamine (1 mM, 20 s), causing no bronchoconstriction before LPS exposure (30 microg ml(-1), 1 h), caused bronchoconstriction at 0.5 and 1 h (P:<0.02) after LPS exposure. This airway hyperreactivity (AHR) recovered by 2 h. In contrast, 48 h after LPS exposure, the response from a previously bronchoconstrictor dose of histamine (3 mM, 20 s) was attenuated (P:<0.01) i.e. airway hyporeactivity (AHOR). 3. Investigation of the cellular content of bronchoalveolar lavage fluid (BALF) from these animals revealed a rapid (0.5 h: 691 fold increase) and progressive neutrophil influx after LPS exposure (24 h: 36.3+/-2.3x10(6) cells per sample), that subsided 48 h later. Macrophages and eosinophils also time-dependently increased (0.5 h: 4.6+/-0.4 and 0.1+/-0.05; 48 h: 31.0+/-6.0 and 1.8+/-0.3x10(6) cells per sample, respectively) after LPS, compared to vehicle exposure (24 h: neutrophils, eosinophils and macrophages: 0.28+/-0.19, 0.31+/-0.04 and 4.96+/-0. 43x10(6) cells per sample, respectively). 4. The combined NO metabolites in BALF, after vehicle (1 h), or LPS (1 h: AHR and 48 h: AHOR) exposure, were respectively increased (41%, P:<0.01), decreased (47%, P:<0.01) and further increased (80%, P:<0.001), compared with naïve animals. 5. Inhaled N(o)-nitro-L-arginine methyl ester (L-NAME: 1.2 and 12 mM, 15 min), reduced BALF NO metabolites 2 h later, but did not cause AHR to histamine (P:>0.05). When L-NAME inhalation followed LPS, AHR was prolonged from 1 h to at least 4 h (P:<0.01). 6. In summary, aerosolized LPS inhalation caused neutrophil and macrophage airways infiltration, and an early development of AHR followed 48 h later by AHOR to histamine. AHR and AHOR coincided with a respective reduction and elevation in airways NO (metabolites). Thus, NO may aid recovery from AHR, as inhibition of its production prolongs AHR. However, NO deficiency alone is not responsible for LPS-induced AHR.

Effects of inhibitors of phosphodiesterase, on antigen-induced bronchial hyperreactivity in conscious sensitized guinea-pigs and airway leukocyte infiltration

1. The aim of this study was to determine the effects of inhibitors of phosphodiesterase (PDE) on the early and late phase bronchoconstriction in sensitized, conscious guinea-pigs and the subsequent development of acute airway hyperreactivity to the inhaled thromboxane mimetic, U46619, and leukocyte infiltration following ovalbumin (OvA) challenge. 2. Following an inhalation challenge with OvA, there was an early bronchoconstriction which peaked at 15 min with recovery after 3-4 h. A late phase bronchoconstriction occurred between 17 and 24 h after challenge. The PDE 4 inhibitors, Ro 20-1724 (3 mg kg-1, i.p.) and rolipram (1 mg kg-1, i.p.) administered 30 min before and 6 h after antigen challenge (double dosing regimen), did not affect the development of the early or late phase responses. 3. Seventeen to twenty four hours following an acute OvA or saline challenge, a consistently greater bronchoconstrictor response to inhaled U46619 was observed in the OvA challenged group. This increase in responsiveness was significantly attenuated by the administration of Ro 20-1724 and rolipram 30 min before and 6 h after antigen challenge (P < 0.05); this was not attributable to a residual bronchodilator effect of these compounds. There was a trend towards inhibition of the hyperreactivity to U46619 by aminophylline but not by the PDE3 inhibitors, siguazodan or SKF 95654. 4. Aminophylline, rolipram and Ro 20-1724 when administered as the double dose regimen attenuated the rise in macrophages, eosinophils and neutrophils recovered in bronchial lavage fluid 17 to 24 h after antigen challenge. 5. The dose of Ro 20-1724 given at 6 h post challenge was essential for attenuation of airway hyperreactivity and to protect against leukocyte influx. 6. In summary, aminophylline, rolipram and Ro 20-1724 have anti-inflammatory effects against antigen-induced airway leukocyte infiltration. Rolipram and Ro 20-1724 additionally attenuated the development of acute airway hyperreactivity, effects which are probably mediated through inhibition of PDE type 4. A dose of PDE inhibitor 6 h after the antigen challenge appears to be essential to achieve this protection. Inhibitors of PDE type 3 were generally without effect. However, there was no effect of rolipram or Ro 20-1724 on the development of either the early or late phase type responses.