Hideyuki Yamauchi

Protection against bradykinin-induced bronchoconstriction in asthmatic patients by neurokinin receptor antagonist

Axon reflex mechanisms may be involved in the pathogenesis of asthma, but there has been no direct evidence that endogenous tachykinins cause bronchoconstriction in asthmatic subjects. We have studied the effect of a tachykinin receptor antagonist (FK-224) on bronchoconstriction induced by inhalation of bradykinin in asthmatic patients. In a double-blind, placebo-controlled, crossover trial, ten subjects with stable asthma were given FK-224 (4 mg) or placebo by inhalation 20 min before challenge with bradykinin (0-1250 micrograms/ml, five breaths of each concentration) given with 5 min intervals. Bradykinin caused dose-dependent bronchoconstriction in all subjects. FK-224 significantly opposed the bronchoconstrictor effect; the geometric mean of the cumulative concentration required to elicit a 35% fall in specific airway conductance was 5.3 micrograms/ml after placebo and 40 micrograms/ml after FK-224 (p < 0.001). Inhalation of bradykinin caused coughing in three subjects, which was inhibited by FK-224 in all three. Antagonism of the tachykinin receptor by FK-224 greatly inhibited both bronchoconstriction and coughing induced by bradykinin in asthmatic patients, suggesting that tachykinin release from the airway sensory nerves is involved in responses to bradykinin. Tachykinin receptor antagonists may be useful in the treatment of asthma.

Angiotensin converting enzyme (ACE) inhibitor-induced cough and substance P.

BACKGROUND: Angiotensin converting enzyme (ACE) inhibitors cause coughing in 5-10% of patients, but the exact mechanisms of this effect are still unclear. In the airways ACE degrades substance P so the cough mechanism may be related to this peptide. METHODS: Nine patients who developed a cough and five patients who did not develop a cough when taking the ACE inhibitor enalapril (2.5 or 5.0 mg/day) for hypertension were enrolled in the study. No subjects had respiratory disease and the respiratory function of all subjects was normal. One month after stopping enalapril, inhalation of hypertonic saline (4%) was performed using an ultrasonic nebuliser for 15-30 minutes to induce sputum. The concentration of substance P in the sputum sample was measured by radioimmunoassay. In four of the nine cases with a cough enalapril was given again for 1-2 weeks and the concentration of substance P in the induced sputum was again measured. RESULTS: One month after stopping enalapril the mean (SE) concentration of substance P in the sputum of the group with a cough was 16.6 (3.0) fmol/ml, significantly higher than that in the subjects without a cough (0.9 (0.5) fmol/ml). All four subjects in the group with a cough who were given a repeat dose of enalapril developed a cough again, but the concentrations of substance P in the induced sputum while taking enalapril (17.9 (3.2) fmol/ml) were similar to the values whilst off enalapril (20.0 (2.5) fmol/ml). CONCLUSIONS: The mechanisms of ACE inhibitor-induced coughing may involve substance P mediated airway priming. However, the final triggering of the ACE inhibitor-induced coughing is unlikely to be due to this peptide.

Involvement of endogenous tachykinins in LTD4-induced airway responses

Leukotriene D4-(LTD4) has been reported to cause tachykinin release from airway sensory nerves. However, the functional significance of endogenously released tachykinins in LTD4-mediated airway responses has not been fully clarified. The aim of this study was to investigate whether LTD4-induced airway responses are due, in part, to tachykinin release in guinea-pigs. Airway plasma exudation and bronchoconstriction were assessed by measuring extravasation of Evans blue dye and by mean pulmonary resistance (RL) in the presence of atropine (1 mg.kg-1 i.v.) and propranolol (1 mg.kg-1 i.v.), respectively. LTD4 (5 micrograms.mL-1 for 1 min) inhalation caused increase in plasma exudation and RL. Capsaicin pretreatment of animals to deplete sensory neuropeptides significantly inhibited LTD4-induced plasma exudation in the main bronchi, but not in the central (cIPA) and peripheral intrapulmonary airways (pIPA). Pretreatment with specific tachykinin neurokinin-1 (NK1)-receptor antagonists, FK 888 (10 mg.kg-1 i.v.) and CP 96345 (4 mg.kg-1 i.v.), also significantly reduced LTD4-induced plasma exudation in the main bronchi, and in the main bronchi and cIPA, respectively. However, these antagonists did not significantly affect the LTD4-induced increase in RL. In contrast, neurokinin-2 (NK2)-receptor antagonist, SR 48968 (0.3 mg.kg-1 i.v.), significantly inhibited the bronchoconstriction after LTD4-inhalation. These results suggest that leukotriene D4-induced bronchoconstriction and plasma exudation in guinea-pigs are, in part, due to tachykinin release from airway sensory nerves.

Repeated allergen exposure enhances excitatory nonadrenergic noncholinergic nerve-mediated bronchoconstriction in sensitized guinea-pigs

The effect of repeated allergen inhalation challenge on the airway excitatory nonadrenergic noncholinergic (e-NANC) nerve-mediated bronchoconstrictor response was studied in ovalbumin (OA) sensitized guinea-pigs. Three weeks after sensitization, OA inhalation, 0.03% for 3 min (challenged group), or saline inhalation (control group) was repeated every day for 4 weeks. The e-NANC nerve function was examined in vitro by means of isometric tension measurement of main bronchi. After pretreatment with atropine (10(-6) M) and propranolol (10(-6) M), we performed electrical field stimulation (EFS) or exogenous neurokinin A (NKA) administration. In the challenged group, EFS-induced main bronchial contraction was significantly greater than that of the control group (p < 0.05 or p < 0.01), but exogenous NKA-mediated responses were almost the same in both groups. The e-NANC-induced main bronchial contractions after EFS were enhanced by pretreatment with the neutral endopeptidase inhibitor, phosphoramidon, to the same degree in the control and challenged groups, indicating that the peptide degradation mechanisms were not impaired even in the challenged group. Substance P immunoreactivities in the lung of the challenged group were significantly higher than those of the control group. These results suggest that chronic airway inflammation after repeated allergen challenge increases excitatory nonadrenergic noncholinergic nerve function, possibly by enhancing sensory neuropeptide production and/or release.

Involvement of apamin-sensitive K+ channels in antigen-induced spasm of guinea-pig isolated trachea.

1 In order to examine whether K+ channels play a role in antigen‐induced airway responses, the effect of K+ channel blockers on antigen‐induced airway smooth muscle contraction and mediator release was examined in vitro in guinea‐pigs actively sensitized with ovalbumin (OA). 2 Tracheal strips from sensitized animals were suspended in organ baths under a resting tension of 1 g and isometric tension was continuously measured. Cumulative concentration‐response curves to OA (0.1–1000 ng ml−1) or histamine (10 nm‐1 mm) were obtained in the presence and absence of K+ channel blockers. 3 OA (10, 100 or 1000 ng ml−1) was incubated with minced lung tissues from the same animals for 15 min in the presence and absence of K+ channel blockers, and released histamine and leukotriene C4 (LTC4) in the incubating medium were measured. 4 Apamin, a small conductance Ca2+‐activated K+ channel (PK,Ca) blocker, (0.1, 0.3 and 1 μm) significantly inhibited OA‐induced smooth muscle contraction, while charybdotoxin (ChTX, 10 nm), an intermediate and large conductance PK,Ca blocker, and iberiotoxin (IbTX, 3 nm), a large conductance PK,Ca blocker, were without effect. Apamin (0.3 μm) had no effect on exogenously administered histamine‐induced airway smooth muscle contraction, suggesting that the inhibition of OA‐induced contraction by apamin did not occur at the smooth muscle level. 5 The inhibition of OA‐induced contraction by apamin (0.3 μm) was not significantly affected by pretreatment with a leukotriene antagonist, ONO‐1078 (10 μm), but was abolished by pretreatment with a histamine H1‐receptor blocker, pyrilamine (1 μm). 6 Apamin by itself (up to 0.1 μm) had no effect on spontaneous histamine release from minced lung tissues. Histamine release induced by low and intermediate concentrations of OA (10 and 100 ng ml−1) was significantly suppressed by apamin pretreatment (P < 0.05 and P < 0.001), whereas LTC4 release was not affected. ChTX (0.1 μm) and IbTX (10 nm) had no significant effect on either spontaneous or OA (100 ng ml−1)‐induced histamine release. 7 These results suggest that apamin partially but substantially inhibits antigen‐induced smooth muscle contraction, presumably by inhibiting antigen‐induced histamine release from airway mast cells through small conductance PK,Ca. closure.