Menopause and subsequent estrogen deficiency have been implicated in the etiology of overactive bladder (OAB) in elderly females. Recently, attention has focused on ischemia of the bladder as a common pathophysiological mechanism for lower urinary tract symptoms (LUTS), including OAB [1]. In the present study, we investigated the effects of ovariectomy (OVX) and estrogen replacement on bladder blood flow (BBF) with an increase in bladder volume.

Virgin Sprague-Dawley rats (24-week old) randomly received a sham operation (SHAM), ovariectomy (OVX), and ovariectomy plus estrogen replacement (OVX+E). In the OVX+E group, the rats were immediately treated with 1mg/Kg weekly injection with β-estradiol for 4weeks.
Four weeks after OVX, rats from the three groups anesthetized with urethane, and the anterior bladder was exposed for the measurement of BBF. Rats were underwent catheter implantation in the bladder . At room temperature, saline was infused at rate of 4ml per hour up to 0.3ml. A laser speckle blood flow imager (OMEGAWAVE, INC. Tokyo, Japan) was used to measure BBF(Fig.1).

When bladder volume was 0ml or 0.1ml, a significant decrease in BBF was observed in OVX rats. BBF in the OVX group was significantly lower than in the SHAM group. This decrease in BBF was significantly suppressed by estradiol treatment . When bladder volume was 0.2ml or 0.3ml, there was no significant difference in BBF(Fig.2).

The present study showed that OVX reduced BBF (ischemia of the bladder)  when bladder capacity was low volume.  Estrogen replacement was shown to restore BBF. Since bladder ischemia is known to cause functional and structural alterations of the bladder and estrogen deficiency induce bladder hyperactivity in our previous data, decreased BBF with low bladder volume may play a potential role in the development of bladder hyperactivity in rats with estrogen deficiency.

This study implicates that bladder ischemia caused by estrogen deficiency was induced  when bladder capacity was low volume.