RESUMO
The present study aimed to evaluate the role of nitric oxide (NO) on hyperpnea-induced bronchoconstriction (HIB) and airway microvascular hyperpermeability (AMP). Sixty-four guinea pigs were anesthetized, tracheotomized, cannulated, and connected to animal ventilator to obtain pulmonary baseline respiratory system resistance (Rrs). Animals were then submitted to 5 minutes hyperpnea and Rrs was evaluated during 15 minutes after hyperpnea. AMP was evaluated by Evans blue dye (25 mg/kg) extravasation in airway tissues. Constitutive and inductible NO was evaluated by pretreating animals with N(G)-nitro-L-arginine methyl ester (L-NAME) (50 mg/kg), aminoguadinine (AG) (50 mg/kg), and L-arginine (100 mg/kg) and exhaled NO (NOex) was evaluated before and after drug administration and hyperpnea. The results show that L-NAME potentiated (57%) HIB and this effect was totally reversed by L-arginine pretreatment, whereas AG did not have effect on HIB. L-NAME decreased basal AMP (48%), but neither L-NAME nor AG had any effect on hyperpnea-induced AMP. NOex levels were decreased by 50% with L-NAME, effect that was reversed by L-arginine treatment. These results suggest that constitutive but not inducible NO could have a bronchoprotective effect on HIB in guinea pigs. The authors also observed that neither constitutive nor inducible NO seems to have any effect on hyperpnea-induced AMP.