Ureteral muscle tone in prevention of vesicoureteral reflux

Three experiments were devised to examine three aspects of the mechanism of the ureterovesical valve in dogs: muscle defects, orientation of muscle in the submucosal segment of the ureter, and the support afforded by the firm bladder base. The ureterovesical valve mechanism of the dog was found to be inefficient when the roof of the submucosal segment was denuded in situ of its muscle. The valve remained efficient when the extravesical ureter, with its circular and oblique arrangement of muscle, was substituted for the normal submucosal ureter with its longitudinally disposed muscle. The efficiency of the ureterovescial junction was not impaired by substituting a floating bed of bladder muscle for the firm platform of the bladder base in which it is normally embedded. The bladder muscle of the hiatus was not effective in the prevention of vesicoureteral reflux if the submucosal segment was rendered inefficient as a sphincter by excision of the muscle in its roof or by excision of the segment. Muscle in the submucosal segment, arranged in either longitudinal or circular fashion, was an effective activator of the mechanical valve. Presumably, the tonic action of the smooth muscle is the activator that ensures the efficiency of the one-way flow flap-trap regulator of the ureterovesical junction.