Vesicourethral smooth muscle: function and relation to structure.

The effects of acetylcholine and norepinephrine on the longitudinal and circular smooth muscle strips from the rabbit bladder body, bladder base, and proximal urethra have been studied and compared. Based on the functional responses that were obtained, it was concluded that the vesicourethral structure can consist of three muscular systems. One system consists of the acetylcholine sensitive detrusor, the deep bladder base, and the longitudinal smooth muscle layer of the urethra. The second muscle system comprises the norepinephrine-sensitive detrusor muscle, the superficial bladder base, the bladder neck, and part of the longitudinal urethral smooth muscle. The third muscle system is the circular urethral musculature, unrelated to the detrusor circular muscle.