Experimental evidence for the existence of a vagino-uterine reflex

The present study was done to investigate the effect of vaginal distention of the uterine myoelectrical activity of nonpregnant and nonlactating female dogs under general anesthesia in a trial to clarify the contradiction reported and to establish the nature of response. It was found that vaginal inflation increased the frequency and amplitude of the uterine basal electrical rhythm significantly (P less than 0.05). Moreover, the enhancement of the myometrial electrical activity recorded in this work was found to occur instantaneously with vaginal inflation (within 3.6 +/- 0.39 s) and decreased rapidly (within seconds) after vaginal deflation. This response was found to be reproducible. However, the excessive repetition of inflation was found to delay the occurrence of change and reduce the response proportionally. Our finding could be regarded as experimental evidence for the existence of a vagino-uterine reflex, in which nervous signals originating in the vagina as a result of stimulation of vaginal stretch receptors by vaginal distention produce a spinal reflex enhancement of the uterine activity. This reflex was abolished by atropinization.