Objective: To investigate the role of nitric oxide (NO) and nitric oxide synthase (NOS) in the pathogenesis of asthma.
Method: 52 guinea pigs were randomly divided into four groups of 13 each: (1) asthmatic group (Group A): Dunkin-Hartley guinea-pigs were injected celiacly with 1 ml of 10% ovalbumin (OA). After 14 days, the animals were inhaled with an aerosol of 1% OA for 40-60 seconds for 10 days every other day; (2) Corticosteroid prevention group (Group CT): As above, just before the animals were inhaled with an aerosol, 0.5 mg/kg dexamethasone were injected celiacly; (3) N-nitro-L arginine prevention group (Group L): As Group A, just before the animals were inhaled with an aerosol, 0.4 mg/kg LNNA were injected celiacly; (4) Controls (Group C): and nitrate (NO2.-/NO3.-) levels in plasma, nitrite bronchoalveolar lavage fluid (BALF) and lung tissues were examined. At the same time, inducible nitric oxide synthase (iNOS) and constitute nitric oxide synthase (cNOS) activity levels in the lung tissues were examined, and the changes of cNOS in the guinea pig asthma model lung tissues were observed using histochemical detection.
Result: All groups had no significant alteration of NO2.-/NO3.- in the plasma (P > 0.05). Group A had increased amounts of NO2.-/NO3.- in the BALF and in the lung tissues compared with the other groups (BALF: Group A 10.2 +/- 1.3, Group CT 7.2 +/- 1.1, Group L 7.3 +/- 1.3, Group C 6.2 +/- 0.8 mumol/L respectively, all of P < 0.01; the lung tissues: Group A 0.89 +/- 0.07, Group CT 0.16 +/- 0.09, Group L 0.24 +/- 0.09, Group C 0.18 +/- 0.05 nmol/mg respectively, all of P < 0.01). Group A also showed increased amounts of iNOS levels in the lung tissues than the other groups (Group A 59 +/- 18, Group CT 10 +/- 5, Group L 12 +/- 7, Group C 10 +/- 5 pmol/mg respectively, all of P < 0.01). Group L showed decreased amounts of cNOS levels in the lung tissues than the Group C (0.8 +/- 0.4, 1.2 +/- 0.4 fmol/mg, P < 0.05). While there were no significant alterations in the other groups (P > 0.05). Elevation of iNOS in the lung tissues was correlated with NO2-/NO3- in the BALF and in the lung tissues (r = 0.714, 0.842, respectively, P < 0.05, 0.01 respectively). NADPHd was found to be a histochemical marker reflecting cNOS activity. It was found that there was no marked alteration of cNOS activity in the Group A, Group CT and Group C, but lower in the Group L.
Conclusion: There is increased production of iNOS in asthmatic guinea pigs, the iNOS produced could cause increased production of NO, and probably cause cytotoxicity and mediate airway hyperresponsiveness. NO and NOS may play an important role in the pathogenesis of asthma.