Effect of extended-term estrogen on voiding in a postpartum ovariectomized rat model

Abstract

Introduction: We tested the hypothesis that extended-term (5-week) estrogen therapy would negatively impact voiding function in a postpartum, ovariectomized rat model.

Methods: Immediately after delivery, 30 primiparous Sprague-Dawley rats underwent intravaginal balloon dilation, followed by ovariectomy 1 week later. Cystometry at postpartum week 2 determined normal or abnormal voiding patterns. After randomization, one-half the normal and abnormal voiding rats received 5 weeks of estrogen therapy, while the remainder received placebo. Estrogen effect was determined by repeat cystometry and immunohistochemical analysis of the urethra and vagina.

Results: Abnormal voiding increased from 60.0% to 73.3% in the estrogen- treated group and declined from 60% to 33% for the placebo group. Rats were then divided into 4 groups for comparison: normal voiding versus placebo (group 1), abnormal voiding versus placebo (group 2), normal voiding versus estrogen (group 3) and abnormal voiding versus estrogen (group 4). Bladder capacity, leak point pressure and maximum voiding pressure were most depressed in group 4. Estrogen treatment was associated with a significant downregulation of alpha(1A) and alpha(1D)-adrenoceptors in the urethral submucosa but an upregulation of nNOS in the urethral smooth muscle.

Conclusion: Extended-term estrogen therapy in a rat model of simulated birth trauma and ovariectomy resulted in a higher rate of incontinence. Immunohistochemical examination demonstrated significant downregulation of urethral alpha(1A)- and alpha(1D)-adrenoceptors and upregulation of neuronal nitric oxide synthase (nNOS) in the urethra of estrogen-treated groups. These studies question the use of hormone replacement therapy in the treatment of postmenopausal incontinence.

Figure 1

Experimental design. AV = abnormal voiding.

Figure 2

Normal cystometry curve. Saline voiding from the urethra only occurs when the bladder contracts at capacity (large arrow) in response to filling (A). Moderate abnormal voiding. Small amount of saline leakage occur several times during filling (small arrows). Larger amounts of saline were voided at bladder capacity (large arrow) (B). Severe abnormal voiding. Saline continues to leak from the urethra (small arrows), inhibiting bladder filling to capacity (C).

Figure 3

Representative α_1A -adrenoceptor staining of cross sections of mid-urethra for placebo-treated (a and c) and estrogen-treated groups (b and d). There is a significant decrease of α_1A (brown) staining in the estrogen- treated group (original magnification a and b 40x, c and d 100x).

Figure 4

Representative α_1A -adrenoceptor staining of vaginal tissue for placebo-treated (a) and estrogen-treated groups (b). There is a much thicker epithelium and subepithelial layer, more muscle in the muscularis layer and increased α_1A (brown) staining in the estrogen treatment group (original agnification 100x).

Figure 5

Representative neuronal nitric oxide synthase (nNOS) staining of midurethral cross-sections for placebo-treated (a and c) and estrogen-treated groups (b and d). There is a significant increase of smooth muscle and epithelial nNOS (brown) staining in the estrogen-treated group (original magnification a and b 40x, c and d 400x).

Figure 6

Representative neuronal nitric oxide synthase (nNOS) staining of the vaginal epithelium for placebo-treated (a) and estrogen-treated groups (b). There is a significant increase of nNOS (brown) staining in the basal layer of epithelium of the estrogen-treatment group (original magnification 100x).