Effects of Bilateral Ovariectomy on the Functional Responses of the Rabbit Bladder Neck and Urethra

Lee, Jeong Gu

Abstract

Pregnancy and menopause induce morphological as well as functional changes in the female urethra. Symptoms of bladder irritation( frequency, urgency) and incontinence are frequent findings in these conditions and are considered to be due to alterations in the distribution of autonomic receptors caused by changes in hormonal milieu. In the present study, the functional responses to field stimulation(FS) and autonomic agonists of the bladder neck and urethra of ovariectomized and virgin New Zealand White rabbits were compared using isolated muscle strips. Passive length tension studies demonstrated substantially greater compliance of the strips ( bladder neck and urethra ) from ovariectomized than from virgin rabbits. FS elicited frequency dependent contractile responses in all strips. The maximal responses to FS were not significantly different in all strips of both groups. Phentolamine was more effective at inhibiting the response to FS of the bladder neck strips from ovariectomized than from virgin rabbits: No significant differences were noted from the urethral strips. Atropine was significantly more effective at inhibiting the response to FS of the strips from virgin than from ovariectomized rabbits. In virgin rabbits, phentolamine was more effectively inhibited the responses to FS for urethral than for bladder neck strips: atropine was more effective at inhibiting the response to FS of bladder neck than in urethra. No such differences were observed in the strips from ovariectomized rabbits. Strips of bladder neck isolated from virgin rabbits responded with significantly greater contraction to phenylephrine than strips from ovariectomized rabbits. No significant dif-ferences were noted in the response to bethanechol The magnitude of field stimulated relaxation was significantly greater in urethral strips isolated from virgin rabbits than in strips from ovariectomized rabbits. Isoproterenol induced slowly developing but significant relaxation ( 55-70 %) of all strips pre-stimulated by phenylephrine. Conclusively, ovariectomy cause profound hor-monal changes resulting in the alteration of the compliance and functional responses of the urethra to various forms of autonomic stimulation. In ovariectomized urethra, decrease of the contractile response to alpha-adrenergic agonist would be a theoretically causative factor of urinary incontinence after menopause. Relaxation of pre-contracted urethra by field stimulation are thought to be the same condition as an active opening of bladder outlet by NANC nitric oxide mediating nerve stimulation in physiologically distended bladder. Consequently, a decrease in the relaxation of urethral strips from ovariectomized rabbits would be a another factor of dysuria or voiding difficulty after menopause.