[Vesicourethral physiology during continence and urination in cats. In vivo and in vitro studies]

The mechanisms implicated in the opening of the bladder neck during voiding are still controversial. We present a study of the reflexes of bladder, urethra and periurethral striated muscles in the cat. The study in vivo shows that a passive muscle tonus of the urethra is able to maintain the continence. During voiding, opening of the bladder outlet is done actively: contraction of the longitudinal and relaxation of the circular muscle layers of the urethra associated with detrusor contraction. There is a local reflex between the urethra, bladder and periurethral striated muscles that completes emptying of the bladder with an interrupted stream. The study in vitro confirms that the 2 muscle layers of the urethra have different innervation: the parasympathomimetic agents act on the longitudinal layer and very weakly on the circular. Both layers react to adrenergic stimulation.