Effect of an H-2 antagonist on gallbladder contraction

Cimetidine, an H-2 blocker, is a potent inhibitor of stimulated acid secretion. Its effects on other tissues have not been completely described. Using strips of guinea pig gallbladder, the effect of cimetidine on histamine-stimulated muscle contraction was tested. Doses of 1.6 × 10^-6, 4.05 × 10^-6, and 8.1 × 10^-6 M histamine acid phosphate produced graded increases of muscle contraction. When these doses were given in combination with 5 × 10^-6 and 5 × 10^-5 M cimetidine, there was a significant increase in muscle contraction. However, when 4.9 × 10^-7 M diphenhydramine hydrochloride, an H-1 receptor inhibitor, was given in combination with histamine, muscle contraction was significantly inhibited. From these data it is concluded that the effects of histamine on gallbladder muscle in vitro are mediated through the H-1 receptor site; however, the H-2 receptor is present and is an inhibitor of muscle contraction.