Oxytocin--a stimulator of directed sperm transport in humans.

Rhythmic peristaltic contractions of the muscular wall of the non-pregnant uterus, as well as rapid sperm transport from the vagina to the Fallopian tubes, have long been documented by means of vaginal sonography and hysterosalpingoscintigraphy. Uterine peristaltic activity reaches a maximum before ovulation and is controlled via oestradiol secretion from the dominant follicle systemically and into the utero-ovarian countercurrent system; it is also enhanced by oxytocin. In this study, the effect of oxytocin and its receptor antagonist atosiban on uterine peristalsis and thus directed sperm transport during the mid and late follicular phases was examined. Atosiban did not show any effect either on frequency or on pattern of the peristaltic contractions. However, oxytocin significantly increased the rapid and directed transport of radiolabelled particles representing spermatozoa from the vagina into the Fallopian tube ipsilateral to the site of the dominant follicle (P = 0.02, 0.04 and 0.02 after 1, 16 and 32 min of documentation respectively). It seems reasonable to assume that oxytocin plays an important, although not critical, role in the mechanisms governing rapid sperm ascension that, at least in humans, were developed to rapidly preserve an aliquot of spermatozoa following intercourse.