The effect of calcium antagonists on allergic pulmonary distress in actively sensitized rats

The induction of allergic pulmonary distress (APD) in ovalbumin sensitive rats can be used as a model of human allergic asthma. In this model, control animals exhibit a rapid decrease in minute volume (Vm) when challenged with ovalbumin (OA) by aerosol (3 % solution). The present study compared the effects of pretreatment with calcium antagonists on the induction of APD. By the aerosol route of administration, 5 min before OA, verapamil HCl (6% solution) significantly (P < 0.05) dampened the allergic response during all 12 min monitored. At an equivalent concentration, diltiazem aHCl significantly (P < 0.05) inhibited the response during 6 of 12 min, whereas nifedipine failed to significantly (P > 0.05) alter the response to OA. Verapamil and nifedipine proved to be equally effective in a dose-dependent manner against OA-induced APD, however, when administered orally (-60 min, 5, 10 or 20 mg/kg). At doses of 10 mg/kg and higher, both calcium antagonists consistently inhibited (P < 0.05) the response. Diltiazem was inactive when administered orally at a dose as high as 20 mg/kg. The present data suggest that the calcium antagonists verapamil, nifedipine and diltiazem, can attenuate APD and therefore might be clinically active agents in the treatment of allergic asthma.