Dissociation of airway inflammation and hyperresponsiveness by cyclooxygenase inhibition in allergen challenged mice.

The aim of the current study was to define how cyclooxygenase (COX)-activity affects airway hyperresponsiveness (AHR) and inflammation using interventions with COX inhibitors at different time points during allergen challenge and/or prior to measurement of AHR in an eosinophil-driven allergic mouse model. Inflammatory cells were assessed in bronchioalveolar lavage (BAL) and AHR was evaluated as the total lung resistance to methacholine (MCh) challenge. Administration of FR122047 (COX-1 inhibitor) during ovalbumin (OVA) challenge and prior to MCh challenge enhanced AHR without affecting the inflammatory cell response. In contrast, administration of lumiracoxib (COX-2 inhibitor) during the same time period had no effect on AHR but reduced the inflammatory cells in BAL. Nonselective COX inhibition with diclofenac both enhanced the AHR and reduced the inflammatory cells. Administration of diclofenac only during OVA challenge reduced the cells in BAL without any changes in AHR, whereas administration of diclofenac only prior to MCh challenge enhanced AHR but did not affect the cells in BAL. The present study implicates distinct roles of prostanoids generated along the COX-1 and COX-2 pathways and, furthermore, that inflammatory cells in BAL do not change in parallel with AHR. These findings support the fact that AHR and the inflammatory response are distinct and, at least in part, uncoupled events.

Hyperosmolarity decreases the relaxing potency of sodium nitroprusside on guinea-pig trachea by the release of superoxide anions.

UNLABELLED: Increased osmolarity of the airway surface has been shown to abolish the airway relaxant effects of inhaled nitric oxide in rabbits in vivo and in guinea-pig trachea in vitro. AIM: In this study, we used a guinea-pig tracheal perfusion method to investigate whether superoxide anions, which rapidly react with nitric oxide, could be responsible for the reduced effect of nitric oxide in hyperosmolar airways. METHODS: Guinea-pig tracheas were constricted with carbachol (CCh) and then subjected to the nitric oxide donor sodium nitroprusside (SNP) under isoosmolar or hyperosmolar conditions. Hyperosmolarity was created by increasing the NaCl concentration of the buffer on the epithelial side of the airway. RESULTS: The relaxation produced by SNP was significantly less following hyperosmolar challenge, with a relaxation by 31 +/- 7% in hyperosmolar conditions as compared to 53 +/- 6% under normal isoosmolar conditions (P<0.05). The experiment was then performed in the presence of superoxide dismutase (SOD) that reduces levels of superoxide anions. SOD restored the relaxing potency of SNP in hyperosmolar conditions back to normal, to 46 +/- 5%. CONCLUSION: This study shows that superoxide anions are responsible for the reduced relaxing potency of the nitric oxide donor SNP following an intraluminal hyperosmolar challenge in guinea-pig trachea in vitro. The finding may form the basis for new treatment of patients not responding to treatment with inhaled nitric oxide.

Hyperosmolarity-induced relaxation and prostaglandin release in guinea pig trachea in vitro.

In this study, a tracheal perfusion apparatus was used to investigate the nature of the relaxing factor released by hyperosmolarity on the epithelial side of guinea pig trachea. NaCl induced concentration-dependent relaxation. This relaxation was not affected when the trachea was preincubated with a vasoactive intestinal peptide (VIP) receptor antagonist or with the nitric oxide synthesis inhibitor N(G)-monomethyl-L-arginine (L-NMMA). When the prostaglandin synthesis was prevented by preincubation with the phospholipase A(2)-inhibitor quinacrine, or the cyclooxygenase inhibitor indomethacin, the maximal relaxation induced by NaCl was suppressed by 50% (P<0.05). Moreover, the prostaglandin E(2) concentration was four times higher (P<0.05) in the organ bath during the relaxations, whereas the nitric oxide concentration remained unchanged. In conclusion, increased osmolarity on the airway surface leads to the release of prostaglandins, which are involved in part in the hyperosmolarity-induced relaxation of airway smooth muscle. This might be relevant for asthmatic patients since prostaglandin may modulate the bronchoconstrictive response to hyperosmolar stimuli and exercise.

Both inhaled histamine and hypertonic saline increase airway reactivity in non-sensitised rabbits.

BACKGROUND: Asthmatics react with bronchoconstriction upon a variety of stimuli, i.e. exercise and hypertonic aerosol challenge. We have previously shown that hyperventilation with dry gas in a rabbit model resulted in a change of the ion content of the tracheal wall. This was followed by a hyperreactive response to histamine. OBJECTIVE: We hypothesised that nebulisation with 3.6% hypertonic saline will be accompanied by a hyperreactive response to histamine in a rabbit model. METHODS: Anaesthetised rabbits were given histamine after nebulisation with hypertonic saline. In addition, repeat nebulisation with hypertonic saline was given with or without histamine between these nebulisations. RESULTS: There was a different response to histamine 10 mg x ml(-1) whether hypertonic saline had been given or not (p < 0.001). Histamine nebulisation, given after hypertonic saline, caused an increase from baseline in resistance of 65 +/- 12 cm H(2)O.litre(-1) x s (mean +/- SEM, p < 0. 001) and a decrease in compliance of 2.3 +/- 0.4 ml x cm H(2)O(-1) (p < 0.001). The corresponding values for the control animals were 10 +/- 4 cm H(2)O.litre(-1) x s (n.s.) and 1.7 +/- 0.2 ml x cm H(2)O(-1) (p < 0.001). At a second nebulisation with hypertonic saline, with a histamine challenge 30 min before, the resistance increased from baseline by 35 +/- 10 cm H(2)O x litre(-1) x s (p < 0.01). This was not observed when no histamine had been given between the hypertonic saline nebulisations. CONCLUSIONS: This study in rabbits shows that hypertonic solutions cause an increase in the responsiveness to histamine and that histamine causes an increase in responsiveness to hypertonic saline. This is similar to the response of asthmatics to hypertonic saline.

Hyperosmolarity reduces the relaxing potency of nitric oxide donors in guinea-pig trachea.

1. Non-responders to inhaled nitric oxide treatment have been observed in various patient groups. The bronchodilatory effect of inhaled nitric oxide was attenuated when the airway lumen was rendered hyperosmolar in an in vivo study on rabbits. We used a guinea-pig tracheal perfusion model to investigate the effects of increased osmolarity (450 mOsm, NaCl added) on the relaxing potency of the nitric oxide donors sodium nitroprusside (SNP) and (+/-)-S-nitroso-N-acetylpenicillamine (SNAP). 2. Under iso-osmolar conditions SNP relaxed the carbachol (CCh, 1 microM) contracted trachea by 83+/-3%. After pretreatment with intraluminal hyperosmolarity SNP relaxed the CCh-contracted trachea by only 31+/-7% (P<0.05). When the trachea was contracted to the same extent under untreated and hyperosmolar conditions, the untreated trachea was completely relaxed by SNP but, after hyperosmolar pretreatment, SNP could no longer relax the trachea. 3. SNAP relaxed the CCh contracted trachea by 27+/-5%. After pretreatment with intraluminal hyperosmolarity, SNAP relaxed the trachea by 11+/-4%, which was less than in the iso-osmolar control (P<0.05). 4. Extraluminal hyperosmolarity did not affect carbachol elicited contraction, and SNP administered externally during extraluminal hyperosmolarity was able to relax the trachea (P<0.05). 5. The cell permeable guanosine 3'5'-cyclic monophosphate analogue 8-Br-cGMP relaxed the CCh contracted trachea in both iso-osmolar (P<0.05) and hyperosmolar conditions (P<0.05). 6. The relaxant effect of nitric oxide donors on tracheal smooth muscle is markedly reduced when the airway epithelium is exposed to hyperosmolar solution.

Increased airway osmolarity inhibits the action of nitric oxide in the rabbit.

Inhalation of nitric oxide (NO) is known to dilate preconstricted airways. In asthmatics, there are large variations in the effect of NO on airway tone. One explanation of these variations may be different degrees of airway wall oedema. The effect of NO inhalation on methacholine (meth)-induced airway constriction was investigated in a rabbit model. Oedema and a change in osmolarity of the airways was achieved by hypertonic saline nebulization and hyperventilation with dry gas. There was an increase in resistance to meth at a concentration of 3 mg x mL(-1), of 86+/-14 cmH2O x L(-1) x s (mean+/-SEM) after oedema formation, compared with 46+/-16 cmH2O x L(-1) x s without oedema. Inhalation of 80 parts per million (ppm) NO failed to counter the increase in resistance due to meth, 92+/-14 cmH2O x L(-1) x s after hypertonic saline nebulization. After hyperventilation of dry gas, the increase in resistance due to meth at 1 mg x mL(-1) was 27+/-11 cmH2O x L(-1) x s with 80 ppm NO and 28+/- 5 cmH2O x L(-1) x s without NO. In conclusion, the relaxant effect of nitric oxide-inhalation on the airway smooth muscle can be blocked by an increase in the osmolarity of the airway surface liquid. The mechanism of this inhibition of nitric oxide remains to be established.

Dry gas hyperpnea changes airway reactivity and ion content of rabbit tracheal wall.

Dry air hyperventilation provokes airway narrowing in asthmatics. The mechanism is thought to involve the release of inflammatory mediators in response to airway osmolarity. The response to inhaled histamine on lung mechanics and the ion content of the airway subepithelial connective tissue after dry gas hyperventilation was investigated in rabbits. Resistance increased more after histamine given after hyperventilation with dry gas compared to humid gas (P < 0.05). Compliance decreased after histamine for both dry and humid gas hyperventilation. The Na, Cl and K content was decreased in the tissue at 4 min (P < 0.001) and nearly returned to resting content at 8 min of hyperventilation with dry gas. The results suggest that dehydration occurred and was followed by oedema formation in the tracheal wall. Thus, the effects of inhaled histamine on airway resistance was amplified. The mechanism involved may be part of the normal defence of the airway to protect against desiccation during hyperventilation with dry air. This response may be exaggerated in asthmatics.