Relative activities of three calcium channel antagonists on histamine, acetylcholine and antigen-induced contractions of guinea pig ileum.

The molar concentrations of verapamil, diltiazem, nifedipine, tripelennamine and atropine necessary to block histamine, acetylcholine (ACH) and ovalbumin-induced contractions of the isolated guinea pig ileum were compared. The calcium blockers inhibited ovalbumin contractions in previously sensitized ilea at lower concentrations than those required to block the phasic component of histamine and ACH contractions. These compounds were, however, more active in blocking the tonic phase of histamine and ACH concentrations than ovalbumin contractions. Tripelennamine was almost as active against ovalbumin contractions as it was against histamine concentrations, while atropine was inactive against ovalbumin. The results are interpreted as being supportive of continued efforts to develop calcium channel antagonists which selectively block the smooth muscle effects of inflammatory mediators.