Effects of long-term treatment with estrogen and progesterone on in vitro muscle responses of the female rabbit urinary bladder and urethra to autonomic drugs and nerve stimulation.

Ovariectomized virginal rabbits were treated with either estrogen or progesterone for 4 to 6 months. In vitro responses of muscle strips of the bladder and circular urethra were examined. Estrogen resulted in bladder contractions in response to noradrenaline and phenylephrine, whereas these agonists were without effect or evoked weak relaxations in castrated animals (and normals). Estrogen also caused a rightward shift of the frequency-contraction curve to nerve stimulation. Progesterone increased bladder sensitivity to contraction-evoking bethanechol. Contractile urethral responsiveness to bethanechol increased after both steroids. Urethral sensitivity to noradrenaline, evoking contraction, increased following estrogen. Further, estrogen abolished the marked relaxatory urethral response to nerve stimulation of castrated (and normal) rabbits and caused contraction only, which was abolished by a combination of alpha-adrenoceptor antagonists and scopolamine. When comparing the present results with those of other studies, it is evident that hormone-induced changes become manifest at an early stage. The present animal study gives support for the use of estrogen in the therapy of stress incontinence and, further, it provides no objections to the use of progesterone in combination with estrogen in this condition.