Effects of Ovariectomy and Estrogen Replacement on Rat Bladder Physiology and Morphology

Lim, Jae Sung; Gil, Geon; Shin, Ju Hyun; Kim, Kang Seop; Koo, Dae Yong; Kim, Jin Kyeom; Sul, Chong Koo; Na, Yong Gil

Abstract

PURPOSES: An overactive bladder is highly prevalent in middle-aged woman, especially during the postmenopausal period. We evaluated the relationship between detrusor overactivity and postmenopausal state and the effects of estrogen replacement for detrusor overactivity caused by the ovariectomy in rat. MATERIAL AND METHODS: Thirty female Sprague Dawley rats were divided into three groups: the control, the ovariectomy group and the estrogen replacement group after the ovariectomy. The ovariectomy and estrogen replacement groups had the bilateral ovariectomies at 12 weeks of age. After 2 weeks, the control and ovariectomy groups were injected weekly with saline, while the estrogen replacement group was injected with estradiol benzoate (500 migrogram/kg) weekly. After 12 weeks, the voiding frequency study was recorded and a cystometrogram was performed while awake. The harvested bladders were used in the carbachol-induced detrusor muscle contraction study and the distribution of estrogen, M2 and M3 muscarinic receptors in the rats' bladder.
RESULTS
The ovariectomy group voided more frequently than the others (p=0.005). During the awake cystometrogram, the detrusor characteristics of the ovariectomy group were a higher mean intervoiding pressure and smaller bladder capacity than the others (p=0.000). There was no significant statistical difference between the control and estrogen replacement group. The other cystometric parameters were not statistically different either. The detrusor muscle contraction study showed no difference between three groups. There was a significant difference in the distribution of M2 and M3 receptors of bladder mucosa between the control and ovariectomy group.
CONCLUSIONS
This study suggested that the detrusor overactivity resulted from increased connective tissue ratio and decreased M2, M3 receptor in the bladder mucosa. Moreover, estrogen replacement in the postmenopausal state had the effect of reversing the physiological and morphological changes caused by an estrogen deficiency in the bladder.