Interaction of Verapamil Hydrochloride and Atropine Sulphate on Histamine-Induced Bronchoconstriction

Abstract

Submaximal histamine dose-response curves were obtained on 34 dogs divided into six groups. These groups were: A (n=6) untreated; B (n=6) after atropine (1 mg/kg); C (n=5) after verapamil inhalation (10 mg total dose); D (n=5) after verapamil inhalation (100 mg total dose); E and F (n=6) as for C and D but pre-treated with atropine (1 mg/kg). Total lung resistance (Rl) was measured in each case at increasing delivered concentrations of inhaled histamine and expressed as a ratio of baseline valve. For each group a composite mean curve was obtained and the maximal recorded responses (mean maximal resistance ratios) for the various groups were compared. It appears that the combination of verapamil inhalation (low dose) and atropine reduced the anticholinergic effect of atropine causing marked bronchoconstriction. This unexpected result depends on the verapamil dose since it was not present at the higher dose (group F).

Effects of three different L-type Ca 2+ entry blockers on airway constriction induced by muscarinic receptor stimulation

“…In addition, as described above, clinically relevant doses may also do this. Similarly, inhaled verapamil has been reported to produce bronchoconstriction 20±22 or reduce atropineinduced relaxant effects, 23 although several reports demonstrated a small bronchodilating action. 24 25 In the present in vitro study, we observed that verapamil 3Q10 ±4 M produced a maximal decrease in tension of tracheal smooth muscle followed by a re-increase of 18%.…”