Plasma estradiol measurements. Female Sprague-Dawley rats were subjected to sham surgery or bilateral ovariectomy. After 2 weeks, sham-operated rats were implanted with subcutaneous osmotic infusion pumps containing vehicle (Control; CONT) or tamoxifen (TMX; 150 μg/day). Ovariectomized rats (OVX) were similarly infused with vehicle. After an additional 2 weeks, vaginal blood flow studies were performed and plasma samples from control (n = 11), tamoxifen-infused (n = 11) and ovariectomized (n = 8) rats were assayed for estradiol (E2) levels by conventional radioimmunoassay. Data are the mean ± SEM and were analyzed by one-way analysis of variance (ANOVA). *p < 0.05 versus control group.