Parallelism between Mechanical and Metabolic Responses to Cholecystokinin and Prostaglandin E2in Extrahepatic Biliary Tract

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Abstract
The mechanical effects of the prostaglandins Ei, E2 and F2u were investigatedin vitroin isolated preparations of guinea‐pig gallbladder, cat gallbladder, and cat sphincter of Oddi. The actions of the prostaglandins, and particularly the effects of prostaglandin Ea, proved similar to those of cholecystokinin,i.e.contraction of the gallbladder and relaxation of the sphincter of Oddi were produced; the responses were not influenced by tctrodotoxin or by blockade of adrenoceptors or cholinoceptors. In the anesthetized cat, prostaglandin E2increased the intraluminal gallbladder pressure and decreased the resistance to flow through the sphincter of Oddi. The contractile responses in guinea pig gallbladder after prostaglandin E2were preceded by a decrease in the tissue levels of cyclic AMP and an activation of phosphodiesterase. The relaxation produced by prostaglandin Ea in the cat sphincter of Oddi was associated with an increase in the cyclic AMP content of the tissue, despite an inci'eased phosphodiesterase activity. These metabolic changes were similar to those observed in response to cholecystokinin. The similarities in mechanical and metabolic effects between prostaglandin Ea and cholecystokinin and the possible role of prostaglandin Ea in mediation of the actions of cholecystokinin on the extrahepatic biliary tract are discussed.