Immunohistochemical reactivity of myometrial oxytocin receptor in extracorporeally perfused nonpregnant human uteri

Introduction: In the pregnant uterus oxytocin and the oxytocin receptor play a major part for uterine contractility and the induction of labor. Clinical evidence implicates that with regard to contractility associated disorders like for example dysmenorrhea also in the nonpregnant and very early pregnant myometrium oxytocin and the oxytocin receptor seem to be more important than believed at the moment. However, little is known about the mutual dependence of the oxytocin receptor, oxytocin and 17-β-estradiol in the nonpregnant myometrium and about the distribution of the oxytocin receptor in the nonpregnant uterus. Therefore, in the present study we investigated in the nonpregnant myometrium if oxytocin receptor expression can be affected by 17-β-estradiol and oxytocin stimulation. Methods: We used a previously established experimental perfusion system for the human uterus. We perfused 10 uteri for 27 h under physiological conditions without 17-β-estradiol (group A, n=5) or with high 17-β-estradiol stimulation (group B, n=5) followed by oxytocin stimulation in both groups in the last 3 h of the experiment. The expression of the myometrial oxytocin receptor in both groups was compared immunohistochemically. Results: In comparison to the negative controls the immunohistochemical reactivity demonstrated increasing oxytocin receptor concentrations with maximum levels under 17-β-estradiol and oxytocin stimulation in the uterine fundus (40% of positive stained cells, p<0.01). However, oxytocin receptor levels did not reach concentrations comparable to specimen of third trimester of pregnancy, which were used as positive controls. Conclusions: Taken together, our data demonstrate that the dynamics of oxytocin receptor expression can be affected by stimulation with 17-β-estradiol and oxytocin not only in the pregnant uterus, but also in the nonpregnant uterus. Therefore, dyscontractile phenomena of the nonpregnant myometrium also may be mediated via 17-β-estradiol, oxytocin and the oxytocin receptor.