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To determine the potential role of neuropeptides in acrolein-induced airway responses, capsaicin-treated guinea pigs were exposed to acrolein aerosol in a regimen causing increased airway sensitivity to substance P. Acrolein exposure resulted in 100% mortality after capsaicin pretreatment compared with only 14% mortality in guinea pigs not pretreated with capsaicin. Acrolein exposure by itself caused marked pulmonary inflammation and large airway epithelial necrosis and denudation. Pretreatment with capsaicin exacerbated these responses throughout the lung. Intravenous acrolein caused an acute dose-related bronchoconstriction in naive guinea pigs that was diminished by capsaicin treatment and potentiated by thiorphan pretreatment, which suggests that arolein exposure causes an acute release of capsaicin-sensitive C-fiber neuropeptides. To determine whether acrolein-induced C-fiber release altered neuronal viability, either rhodamine or Fast Blue dye was instilled intratracheally into vehicle- or acrolein-exposed guinea pigs. Acrolein exposure did not reduce the neuronal uptake or retrograde transport of these dyes, as indicated by the number of fluorescent cell bodies in the nodose ganglia. To determine the functional state of airway neurons, the dose response to intravenous capsaicin was measured in vehicle-exposed and acrolein-exposed guinea pigs; no differences were observed. Thus, acrolein appears to activate airway C-fibers, which release neuropeptides that are protective against this insult, with no suggestion of an accompanying reduction in C-fiber function.

The effects of acrolein exposure on airway responses to intravenous substance P were determined in guinea pigs exposed to vehicle or 1.6 ppm acrolein for 7.5 h on 2 consecutive days and examined 1, 4, 8, 15, and 28 days after exposure by use of pulmonary mechanics and bronchoalveolar lavage (BAL). Lung, trachea, liver, and BAL fluid were also assayed for neutral endopeptidase (NEP) activity 1, 7, and 28 days after exposure. Pulmonary inflammation and epithelial damage were prominent 1 day after acrolein exposure. NEP activity was decreased in the lungs, trachea, and liver 1 and 7 days after acrolein. Twenty-eight days after exposure, NEP activity in the lungs and liver was not significantly different in vehicle- and acrolein-exposed guinea pigs but was still reduced in tracheal tissue. The BAL NEP activity in acrolein-exposed guinea pigs was approximately twice that of vehicle control guinea pigs at all three time points. Acrolein caused a prolonged increase in airway sensitivity to substance P. Experiments performed in the presence of thiorphan suggested that the acrolein-induced reduction in NEP may contribute to increased airway sensitivity to aerosolized substance P, but the increase in airway sensitivity to intravenous substance P may occur by additional mechanisms.

(S)-N-(4-benzoylphenyl)-3,3,3-trifluoro-2-hydroxy-2-methyl-propionamide (ZD6169) is a novel ATP-sensitive potassium channel opener. Bladder activity and selectivity after oral dosing were studied in conscious, normotensive rats and dogs by monitoring cystometric and cardiovascular (CV) parameters. The reference ATP-sensitive K+ channel opener cromakalim was also evaluated in this study. ZD6169 significantly reduced micturition frequency in rats (ED50 = 0.16 mg/kg), but its effect on CV parameters was minimal (ED20 = 30 mg/kg), yielding a selectivity dose ratio of 187. The duration of action was between 7 and 24 hr at doses of 0.3 and 3 mg/kg, but it was more than 24 hr at 10 mg/kg. The ED50 value for bladder activity in dogs was less than 1.0 mg/kg, and the ED20 value for CV activity was slightly greater than 15 mg/kg but less than 20 mg/kg; the selectivity ratio was greater than 15. A significant improvement in bladder compliance was noted in dogs with ZD6169, and the bladder activity in rats was blocked by i.v. glibenclamide (3 mg/kg). Cromakalim had a bladder profile similar to that of ZD6169 but appeared to be more selective for CV parameters. In conclusion, ZENECA ZD6169 is a unique ATP-sensitive K+ channel opener with in vivo selectivity of relaxing bladder smooth muscle. This agent has the potential for treating patients with urge incontinence.