Relaxation of guinea-pig stomach by bradykinin

Intraluminal pressure changes were recorded from guinea-pig stomachs in vitro. Bradykinin (Bk) (0.4-9.6 nM) was generally found to produce a biphasic response (relaxation followed by contraction) in bathing solutions containing 1.1 mM calcium chloride. In bathing solutions containing 5.2 mM calcium chloride a relaxation without contraction was the most common observation. Relaxations to Bk were unaffected by selective concentrations of tetrodotoxin (5.6 microM), phentolamine (5.0-50.0 microM) and propranolol (5.0-50.0 microM). During virtually complete desensitization to Bk produced by 3 cumulative doses of 6.4 nM, relaxations to vagal stimulation were only reduced by 24.2% and those to adrenaline (2.0 microM) by 25.9%, indicating that Bk is unlikely to be the inhibitory transmitter released during vagal stimulation. Relaxations to ATP (10 microM) were reduced by 89.4% suggesting that Bk and ATP share a common step in the production of relaxation.