The influence of ovariectomy and estradiol replacement on urinary bladder function in rats

Female Fischer 344 rats were ovariectomized or sham operated and treated with oil or estradiol cypionate (100 mg./100 gm./month) for two or four months. Rats were then placed in metabolism cages for measurement of micturition characteristics, and bladders were removed for bladder strip studies. Ovariectomy had no effects on micturition characteristics. However, estradiol treatment of ovariectomized rats caused significant increases in water consumption and urine excretion, and in mean and maximal micturition volumes compared to both ovariectomized and sham-operated rats. These effects were more pronounced at four months. Estradiol treatment also caused significant increases in bladder body mass, while ovariectomy was without effect. Two months after ovariectomy and/or estradiol treatment, there were no differences in contractile responses of bladder body or base strips to contractile agents when compared to shams. However, after four months, ovariectomy caused significant decreases in contractile responsiveness to nerve stimulation. ATP, carbachol, and KCl compared to sham-operated rats. Estradiol treatment caused increased responsiveness to nerve stimulation, ATP, carbachol, and KCl compared to ovariectomized rats, and to carbachol compared to sham operated rats. Possible causes for the effects of ovariectomy on bladder contractility include decreases in calcium influx. Although estradiol reversed the effects of ovariectomy on bladder function, in addition we observed some indirect effects which were probably the result of estradiol-induced polyuria and increases in bladder mass.