Uterine peristalsis during the follicular phase of the menstrual cycle: effects of oestrogen, antioestrogen and oxytocin

Uterine peristalsis directing sustained and rapid sperm transport from the external cervical os or the cervical crypts to the isthmic part of the tube ipsilateral to the dominant follicle, changes in direction and frequency during the menstrual cycle, with lowest activity during menstruation and highest activity at mid cycle. It was therefore suggested that uterine peristalsis is under the control of the dominant follicle with the additional involvement of oxytocin. To test this hypothesis, vaginal sonography of uterine peristalsis was performed in the early, mid and late proliferative phases, respectively, of cycles of women treated with oestradiol valerate and with human menopausal gonadotrophin following pituitary downregulation, with clomiphene citrate and with intravenous oxytocin, respectively. Administration of oestradiol valerate resulted in oestradiol serum concentrations comparable with the normal cycle with a simulation of the normal frequency of peristaltic contractions. Elevated oestradiol concentrations and bolus injections of oxytocin resulted in a significant increase in the frequency of peristaltic contractions in the early and mid follicular phases, respectively. Clomiphene tended, though insignificantly so, to suppress the presence of elevated oestradiol concentrations. In the late follicular phase of the cycle extremely elevated oestradiol concentrations as well as the injection of oxytocin resulted only in an insignificant further increase of peristaltic frequency. In the normal cycles, as well as during extremely elevated oestradiol concentrations and following oxytocin administration, the peristaltic contractions were always confined to the subendometrial layer of the muscular wall. The results and the review of the literature indicate that uterine peristalsis during the follicular phase of the menstrual cycle is controlled by oestradiol released from the dominant follicle with the probable involvement of oxytocin, which is presumably stimulated together with its receptor within the endometrial-subendometrial unit and therefore acting in an autocrine/paracrine fashion. Since unphysiological stimulation with oestradiol and oxytocin did not significantly increase the frequency of uterine peristalsis in the late follicular phase of the cycle it is assumed that normal preovulatory frequency of uterine peristalsis is at a level which cannot be significantly surpassed due to phenomena of refractoriness of the system.