Abstract
The extracellular calcium antagonists, nifedipine and verapamil, the mixed extra/intracellular calcium antagonist diazoxide and the intracellular calcium antagonist TMB-8 were studied for their effects on histamine-induced bronchospasm in guinea pigs and on antigen-induced bronchospasms in guinea pigs and rats when administered directly to the tracheobronchial tree. Nifedipine and verapamil inhibited histamine and antigen-induced bronchoconstriction in guinea pigs, and verapamil was effective in preventing antigen-induced bronchospasms in rats. However, using doses of the extracellular blockers which produce these pulmonary effects, significant reduction of blood pressure occurred in both guinea pigs and rats. Diazoxide was inactive against histamine and antigen-induced bronchoconstrictions in guinea pigs. TMB-8 was inactive against histamine and antigen-induced bronchospasm in guinea pigs and rats. These studies demonstrate the antibronchoconstrictor activity of extracellular Ca2+ antagonists in guinea pigs and rats, but indicate that intracellular Ca2+ antagonists are not antibronchospastic agents in these species in vivo.
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