A partial involvement of histamine in ultrasonically nebulized distilled water-induced bronchoconstriction in guinea-pigs

1 Inhalation of ultrasonically nebulized distilled water (UNDW) can induce bronchoconstriction only in asthmatics, but mechanisms of the response are not well known. We recently reported a guinea-pig model of UNDW-induced bronchoconstriction (UNDW-IB) in which UNDW induces bronchoconstriction when UNDW is inhaled 20 min after a challenge with aerosolized ovalbumin (OA) in passively sensitized, anaesthetized and artificially ventilated guinea-pigs. 2 To elucidate the role of histamine in the UNDW-IB, we examined the effects of antihistamines, diphenhydramine hydrochloride (DH) and chlorpheniramine maleate (CP), and measured histamine content in bronchoalveolar lavage fluid (BALF) in the animal model. 3 DH in doses of 0.1, 1.0 and 10 mg kg(-1) and CP in doses of 0.01, 0.1 and 1.0 mg kg(-1) administered intravenously 15 min after the OA challenge partially reduced the UNDW-IB at 1 and 2 min after the UNDW inhalation in a dose-dependent manner. Histamine content in BALF recovered 10 min after the UNDW inhalation following the OA provocation was significantly increased compared with that after saline inhalation and before the UNDW inhalation following the OA challenge. 4 Intravenous atropine in a dose of 0.5 mg kg(-1) or inhaled disodium cromoglycate in concentrations of 1 and 10 mg ml(-1) did not alter the UNDW-IB. 5 These results suggest that histamine is involved in part in the UNDW-IB in our animal model.