Effect of estrogen on sensitivity of rabbit bladder and urethra to phenylephrine

The sensitivity of alpha-adrenoceptors to phenylephrine as indicated by the ED50 of the rabbit bladder and urethra was compared for segments in vitro from control (estrous), ovariectomized, ovariectomized-estrogen-treated, and pregnant animals. In control animals there was a trend for urethral segments to be more sensitive to phenylephrine (lower ED50) than bladder segments. This difference was abolished by castration, which decreased the sensitivity of the anular urethral segment, and by pregnancy, which tended to enhance the sensitivity of the bladder. The tension generated by bladder segments was enhanced by pregnancy and tended to be decreased by castration. The effects of castration tended to be reversed by treatment with estrogen (1 microgram per kg of body weight per day for 14 days). These data indicate that estrogen can influence the response of the urethra and urinary bladder to alpha adrenergic stimulation.