Effects of 17β-Estradiol on Spontaneous Myometrial Contractions in Overiectomized Rats

The aim of this study was to evaluate the effect of injecting different doses and time intervals of 17β-estradiol on spontaneous myometrial contractions of ovariectomized rats. Three to 6 months old 72 female Sprague Dawley rats, weighing 270 ± 20 g, were used in the current study. The ovariectomized rats were randomly assigned to a control (Ov) and three experimental groups (17β-estradiol injected) of 18 rats each. Rats in the Ov group received daily sesame oil (0.2 ml, IM), whereas each rat in the three experimental groups was treated with daily 25, 50 and 100 μg estradiol (IM), respectively. Each group was further divided into 3 subgroups: 6 rats in each group were sacrificed by cervical dislocation at 18, 90 and 162 hr. In order to determine endogenous nitric oxide activity, the L-arginine solution was used. Sodium nitroprusside (SNP) was used for evaluation of the exogenous nitric oxide pathway. In addition, L-NNA (nitro-N-arginine) treatment was applied in order to determine the effect of endogenous NO at the receptor level. Immunohistochemical evaluation was performed to determine the cGMP-PK1 expression from the uterus samples. In the current study, estrogen treatment increased spontaneous myometrial contraction in a dose and time-dependent manner. Moreover, estrogen treatments inhibited L-arginine-NOS-NO-cGMP pathway. On the other hand, estrogen failed to have any effect on cGMP-PK1 expression in uterine longitudinal smooth muscles. Thus, 17β-estradiol treatments increased the uterine smooth muscle cell contractions. The treatments also inhibited L-Arginine-NOS-NO-cGMP-PK1 pathway. However, our results indicated that 17β-estradiol did not show its effect through cGMP-PK1