Antihistaminic properties of cicletanine in human isolated coronary arteries.

Cicletanine was tested as an antagonist of the various actions of histamine in coronary artery rings isolated from old (mostly atherosclerotic) and young (non-atherosclerotic) patients. Histamine mainly induced concentration-dependent contractions in arteries from old patients. Cicletanine antagonized this effect with a pA2 value of 6.9 (slope factor of 0.94), revealing in some cases a relaxant effect of histamine. In addition, cicletanine increased the threshold concentration of histamine required to trigger spastic, indomethacin-sensitive rhythmic contractions in (some) rings of the oldest patient. At variance with what occurred in coronary rings from old patients, the predominant effect of histamine in rings from young patients was relaxation. This relaxation remained unaltered by cicletanine (1 microM). As a whole, these results extend the histamine H1 antagonistic activity of cicletanine to human coronary arteries. If histamine is involved in the promotion of vasospasm, then cicletanine could be of potential benefit to patients, without apparently affecting the relaxant response to histamine in non-cardiac patients.