Poster 12: Comparative Effects of 1- and 5-Week Ovariectomy on Contractile Function of the Rabbit

Abstract

OBJECTIVE: The urinary bladder can be considered a target organ for the actions of estrogen. Decreases in circulating estrogen postmenopause have been associated with urinary bladder dysfunctions, including incontinence and detrusor instability. Recent studies indicate that these changes can occur quite quickly when circulating estrogen decreases after ovariectomy. The current study was designed to compare the effects of ovariectomy at 1 and 5 weeks on contractile responses of the rabbit detrusor. METHODS: Female New Zealand white rabbits were ovariectomized and evaluated for the in vitro effects on contractile function (field stimulation [2, 8, and 32 Hz], carbachol [10 uM], ATP [1 mM], and KCl [120 mM]) at 1 and 5 weeks after ovariectomy (n=4–6 rabbits for each group). A control group of 4 rabbits was evaluated simultaneously. RESULTS: 1) Ovariectomy resulted in no significant change in bladder weight at either 1 or 5 weeks. 2) Both 1- and 5-week ovariectomy resulted in decreased maximal contractile responses to 8 and 32 Hz FS. No significant decreases were noted for the maximal responses to ATP, carbachol, or KCl. 3) Both 1- and 5-week ovariectomy resulted in significant decreases in the rate of tension generation for 32 Hz. 4) One-week ovariectomy resulted in a significant decrease in the rate of tension generation to ATP, whereas 5-week ovariectomy resulted in significant and substantial decreases in the rate of tension generation for ATP, carbachol, and KCl. CONCLUSIONS: These findings demonstrate that bladder contractile function is significantly affected by ovariectomy. In previous studies, we have demonstrated that the first sign of contractile dysfunction is a decrease in the rate of tension generation rather than decreases in the maximal contractile responses. These studies indicate that the longer the rabbit is ovariectomized, the greater the level of contractile dysfunctions. Decreased contractile function of the urethra especially may relate to the increased incidence of incontinence postmenopause.