Resistance and sphincter-like properties of the cystic duct.

The canine cystic duct, like that in man, has an extremely thin layer of muscle deep to the mucosal layer, surrounded by a dense layer of collagen fibers. The resistance to flow through the duct was studied in 16 anesthetized dogs by perfusing the duct with saline solution at constant pressure and recording the flow rate of the solution. The flow rate varied with respiratory movements, but there were also nonrespiratory variations which might be due to spontaneous sphincter-like contractions. Significant reductions in flow through the duct followed systemic intravenous or local intra-arterial injections of morphine or pharmacologic concentrations of adrenaline or cholecystokinin. It was concluded that an extremely small amount of muscle in the wall of the duct was capable of sphincter-like activity. The resistances to flow were the same in either direction through the duct, an indication that the prominent mucosal folds, valves of Heister, did not function as unidirectional valves. In view of the high resistance to flow through the duct and the possibility that sphincter-like activity may also occur under physiologic conditions, the function of the duct requires more attention than it has received in the past.