Release of endothelin-1 into rat airways following Sephadex-induced inflammation; modulation by enzyme inhibitors and budesonide.

The intratracheal (i.t.) instillation of Sephadex beads into rat induced inflammation and a 30-fold increase in the endothelin-1-like immunoreactivity (ET-1-LI) of broncho-alveolar lavage fluid. The levels were highest 24 h after the instillation and had declined significantly after 48 h. At a dose of 1 mg kg-1 i.t., the glucocorticosteroid budesonide almost abolished this response. Phosphoramidon, which inhibits neutral endopeptidase, an enzyme reported to degrade ET-1 and also to inhibit the endothelin-converting enzyme, potentiated the Sephadex-induced rise in ET-1-LI. Chymostatin and heparin, which are reported to reduce the formation of ET-1, did not affect the increase in ET-1-LI. The present model represents a very reactive system for analyzing the changes in ET-1 levels during inflammation.

Effect of allergen provocation on inflammatory cell profile and endothelin-like immunoreactivity in guinea-pig airways.

The effect of allergen challenge on the number of leucocytes and the concentration of endothelin 1-like immunoreactivity (ET-LI) in bronchoalveolar lavage fluid (BALF) was investigated in guinea-pigs sensitized to Ascaris suum. The animals were twice exposed to allergen aerosol. All animals responded to the second challenge with bronchoconstriction. Twelve hours later, a significant increase in the number of eosinophilic granulocytes in BALF, compared to unsensitized and unprovoked control animals, was noted. Twenty-four hours after provocation, there was also an elevation of ET-LI concentration and content of neutrophils. During the first day post-challenge, the ET-LI values were moderately correlated to the eosinophil levels. One week after challenge, the ET-LI level and the neutrophil count did not differ from corresponding values in control animals whereas the number of eosinophils remained elevated. Pretreatment with dexamethasone before the second allergen challenge did not consistently affect the parameters studied during the first 24 h. Bronchoconstriction induced by carbachol aerosol affected significantly neither the ET-LI concentration nor the number of inflammatory cells in BALF. It is concluded that the allergen-induced inflammation in the guinea-pig airways causes an elevation in the ET-LI concentration in BALF and that this is moderately correlated to the influx of eosinophils during the first 24 h.

Regulatory effects of aerosolized budesonide and adrenalectomy on the lung content of endothelin-1 in the rat.

This study was designed to investigate the effect of inflammation and glucocorticosteroids (GCS) on the content of endothelin-1-like immunoreactivity (ET-LI) in the rat lung. Following intratracheal instillation of Sephadex beads, which induces a long-lasting inflammation in the lung, there was an increase in the lung content of ET-LI measured by RIA. This increase was abolished by locally administered aerosolized budesonide at doses that had only minor systemic effects (measured as a reduction in body weight). In a second series of experiments, rats were subjected to surgical adrenalectomy in order to reduce the levels of endogenous GCS. This procedure elevated the ET-LI levels in the lungs. In contrast, neither adrenalectomy nor high doses of budesonide administered systemically affected the concentration of ET-LI in the kidney. It is concluded that the lung ET levels are elevated in inflammatory conditions and that this increase is highly sensitive to locally administered GCS. Endogenous GCS may, directly or indirectly, play a role in the regulation of lung ET content but there seems to be no general GCS effect on basal tissue levels of ET.

Regulation of lung endothelin content by the glucocorticosteroid budesonide.

Intratracheal instillation of Sephadex beads induced a long-lasting inflammation in the rat lung as seen by an increase in lung weights. Repeated instillation enhanced this reaction and increased lung endothelin-1 content 3.5 times. Budesonide given s.c. abolished these effects and even reduced basal endothelin-1 content by 72%. The tissue content of the sensory neuropeptide neurokinin A were unaffected by both treatments. Endothelin has been proposed to play a part in the pathogenesis of bronchial asthma. If it is so, the ability of budesonide to reduce endothelin-1 content could thus be added to the list of beneficial effects of glucocorticosteroids in these conditions.

Relationship of airway responsiveness to agents causing bronchoconstriction and cough in sensitized guinea-pigs.

The relationship between airway responsiveness to bronchoconstrictor- and cough-inducing stimuli has been examined in Ascaris suum-sensitized conscious guinea-pigs. Guinea-pigs were sensitized to Ascaris suum [4000 PNU and 100 mg Al(OH)3 i.p. on days 1 and 7] and then challenged with aerosolized antigen on days 21, 28 and 35. At day 35, antigen-exposure produced an early bronchoconstrictor response (EBR) and in about 50% of the animals also a late bronchoconstrictor response (LBR) commencing 4-8 h later. The bronchial responsiveness to inhaled histamine was increased in sensitized guinea-pigs and increased further 20-24 h after acute antigen challenge. Guinea-pigs developing only EBR were equally sensitive to histamine as those having both EBR and LBR. In contrast, the cough and reflex bronchoconstriction produced by inhaled citric acid (0.40 M, acting on capsaicin-sensitive sensory neurons) and cigarette smoke (3 min exposure; exciting both capsaicin-sensitive neurons and rapidly adapting stretch receptors) were not altered by sensitization. Furthermore, acute antigen challenge did not alter the effect of citric acid as measured 24 h later. The antigen-induced airway hyperresponsiveness to histamine was not accompanied by an altered sensitivity of airway sensory nerves mediating cough (and reflex bronchoconstriction), demonstrating that bronchial- (airway obstruction) and sensory- (cough) hyperresponsiveness involve separate and independent mechanisms.

A comparison of the effect of inhaled diuretics on airway reflexes in humans and guinea pigs.

The effects of nebulized diuretics on citric acid-induced cough and airway obstruction in guinea pigs and capsaicin-induced cough and increase in airway resistance in humans have been studied. Half-maximum inhibition of cough in the guinea pig was produced by 1.3 mM furosemide and 0.25 mM hydrochlorothiazide. Cough was inhibited by 78 +/- 9% by 3 mM furosemide (P less than 0.05) and 89 +/- 11% by 3 mM hydrochlorothiazide (P less than 0.01). At the same time, airway obstruction was inhibited by 50 +/- 9% (P less than 0.001) and 42 +/- 15% (P less than 0.05), respectively. Nebulized furosemide (3 mM) was without effect on the airway obstruction produced by inhaled histamine or acetylcholine in the guinea pigs. Intravenously administered furosemide (270 nmol/kg) did not affect citric acid-induced responses. In humans, aerosolized furosemide (9 mM) and hydrochlorothiazide (3.4 mM) reduced the percent increase in respiratory resistance from 22.1 +/- 3.7 and 15.6 +/- 3.4 to 10.5 +/- 4.9 and 9.4 +/- 3.3%, respectively (P less than 0.05), but were without effect on cough due to capsaicin. Thus both furosemide and hydrochlorothiazide inhibited airway obstruction in the guinea pig and reduced the capsaicin-induced increase in airway resistance in humans. However, whereas coughing was inhibited in the guinea pig, neither drug affected cough in humans. This difference in the action of the loop diuretic and thiazide, which interact differently with Na(+)-K(+)-Cl-transport within the airway mucosa, on the cough and airflow obstruction in guinea pig and humans supports the view that different sensory limbs are involved in these reflexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective inhibition of cough and bronchoconstriction in conscious guinea pigs.

In guinea-pigs citric acid-induced cough and bronchoconstriction were inhibited by beta 2-agonist and xanthine drugs. Lidocaine inhibited only cough. Cromoglycate and ipratropium bromide inhibited only bronchoconstriction. We conclude that cough and bronchoconstriction in guinea-pigs are distinct reflexes and that the inhibitory pharmacology of these airway reflexes may agree in many respects, with that observed in asthmatic subjects.

Cigarette smoke-induced changes in guinea-pig airway responsiveness to histamine and citric acid.

The effect of 50 min cigarette smoke exposure on airway responsiveness to the bronchoconstrictor and tussive effects of histamine and citric acid has been examined in guinea-pigs. Intravenous histamine increased intratracheal pressure (ITP) in anaesthetized guinea-pigs and the dose-response curve was significantly (P less than 0.05) steeper in cigarette smoke- than in air-exposed animals. ED50 values were 11.4 nmol kg-1 (7.4-16.8, 95% confidence interval) and 42.5 nmol kg-1 (28.8-61.4, 95% confidence interval), respectively (P less than 0.05) in smoke- and air-exposed guinea-pigs indicating an enhanced reactivity. However, the sensitivity to intravenous histamine was not changed by the cigarette smoke exposure, and the maximum increase in intratracheal pressure was the same as in control animals (air: 247 +/- 21%, n = 4; smoke: 223 +/- 18%, n = 7). The cigarette smoke-induced hyperresponsiveness to intravenous histamine was not altered by pretreatment with nebulized lidocaine (0.20 M), ipratropium bromide (0.30 mM) or cromoglycate (0.06 M), suggesting that a neural reflex is unlikely to be involved in the development of hyperresponsiveness. Conscious, smoke-exposed guinea-pigs had a significantly (P less than 0.001) reduced responsiveness to citric acid (0.40 M) and cigarette smoke. Both cough and bronchoconstriction were suppressed for about 1 h, but unchanged 24 h after exposure. The hyporesponsiveness to citric acid was inhibited by atropine (1.4 mumol kg-1 i.p.) and may therefore, at least in part, be due to increased airway secretions. The present data demonstrate that inhalation of cigarette smoke may alter guinea-pig airway responsiveness to tussive and bronchoconstrictor stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperresponsiveness to tussive stimuli in cigarette smoke-exposed guinea-pigs: a role for capsaicin-sensitive, calcitonin gene-related peptide-containing nerves.

Environmental pollutants may induce airway hyperresponsiveness to bronchonconstrictor stimuli, but if there is a concomitant change in other defensive reflexes, like the cough reflex, is not known. We have examined how two weeks' exposure to cigarette smoke influences airway sensitivity to inhaled irritants acting mainly through capsaicin-sensitive sensory neurons (citric acid, capsaicin) or rapidly adapting stretch receptors (cigarette smoke, histamine). Guinea-pigs were exposed, over a period of one hour, to cigarette smoke or room air, twice daily for 2 weeks. Twenty-four hours after the end of the smoke exposure coughing produced by nebulized citric acid (0.40 M) and capsaicin (30 microM) was enhanced 3.7 (P less than 0.001) and 2.5 (P less than 0.05) times, respectively, whereas the cigarette smoke-induced cough was unchanged. The enhanced responsiveness gradually returned to normal over a period of three weeks and was not mediated by cyclo-oxygenase products since it was not affected by indomethacin (3 mumols kg-1). In contrast, the broncho-constrictor responses to citric acid, capsaicin, cigarette smoke and histamine (0.70 mM) were not altered by inhalation of cigarette smoke. Smoke-exposed animals had a significantly (P less than 0.05) increased amount of calcitonin gene-related peptide-like material (CGRP, contained in capsaicin-sensitive sensory neurons) in tracheal tissue, suggesting that chronic irritation stimulates peptide synthesis. The amount of neuropeptide Y-like material (in autonomic motor nerves) in pulmonary tissue was not changed indicating some 'specificity' in the irritative effect of smoke. It is concluded that prolonged exposure to cigarette smoke produces a tussive hyperresponsiveness that seems to involve specifically capsaicin-sensitive, CGRP-containing sensory neurons mediating cough. The present data demonstrate the development of a 'sensory' hyperresponsiveness, separate from airway hyperresponsiveness to bronchoconstrictor agents.