Inhibitory effect of low molecular weight heparin on the bronchoconstriction in ovalbumin-sensitized guinea pigs after antigen exposure

To elucidate the effect of low molecular weight heparin (LMWH) on the bronchoconstriction, we examined the serial changes of the resistance of respiratory system (Rrs) in ovalbumin (OA)-sensitized guinea pigs after antigen exposure. After sensitization of guinea pigs with repeated OA inhalation, Rrs was measured at immediate asthmatic response (IAR) and late asthmatic response (LAR) with or without LMWH inhalation. Alteration in the number of inflammatory cells of the lung by LMWH inhalation was examined in the broncholaveolar lavage fluid (BALF) and in the histological sections of airway walls. Peak Rrs at 1 min up to 9 min, except 8 min, after antigen exposure significantly decreased by the pretreatment with LMWH inhalation as compared with saline inhalation. Peak Rrs at LAR (after 4 hours up to 24 hours, except 6 hours) also showed a significant decrease in the pretreatment with LMWH inhalation. Pretreatment of LMWH exhibited a decrease of eosinophil percentage in BALF (5.5 +/- 1.2% from 8.2 +/- 0.4% in saline inhalation) and a decrease of infiltrated eosinophil count in airway walls (71.0 +/- 7.3 from 155 +/- 15.8 in saline inhalation). These data show LMWH might play an important role as an inhibitory factor to bronchial asthma.