Vaginal hyperalgesia in a rat model of endometriosis.

This study examined whether a rat model of surgically-induced endometriosis that reduces fertility also evokes vaginal hyperalgesia along with changes in vaginal compliance. In nine rats trained to escape vaginal distention, percent escape responses to different volumes of vaginal distention were measured for 2.5 months before and after endometriosis or sham surgery. Vaginal pressures were also measured simultaneously to provide an estimate of vaginal compliance. Endometriosis (or sham) was induced by autotransplantation of small pieces of uterus (or fat) on mesenteric cascade arteries, abdomen, and ovary. Escape responses were significantly increased only in rats whose autotransplants had formed cysts. Vaginal pressures, however, remained unchanged. This vaginal hyperalgesia may involve a process of viscero-visceral referred hyperalgesia.