Effects of morphine on the guinea-pig biliary tract

The effects of morphine on the terminal bile duct (terminal cavity and ampulla) and gallbladder were investigated in vitro. Morphine, above 10(-7) M, inhibited spontaneous contraction of the terminal cavity and ampulla. The contraction evoked by transmural stimulation, which was inhibited by atropine and tetrodotoxin, was dose dependently suppressed by morphine above 10(-10) M in the amp]ulla, and above 10(-8) M in the terminal cavity. Morphine did not affect the acetylcholine (ACh)-induced contraction, but reduced the contraction evoked by 5-hydroxytryptamine (5-HT) which was suppressed by atropine. In the gallbladder, morphine did not affect the spontaneous contraction, or the contraction evoked by transmural stimulation, ACh, or 5-HT. The 5-HT-induced contraction was not affected by atropine. The results show that morphine reduces acetylcholine release from cholinergic neurons in the terminal bile duct, but not in the gallbladder. The contraction induced in gallbladder by 5-HT was not mediated by cholinergic neurons.