Change in morphology and oxytocin receptor expression in the uterine blood vessels during the involution process

The histological changes in uterine blood vessels during pregnancy have been well investigated, but there have been few reports focusing on the changes in blood vessels during the involution process, especially within the first 24 h. We observed the process of uterine involution, focusing on the vessels of the resected uterus.

Paraffin-embedded uterine samples from 15 patients who underwent hysterectomy because of severe cervical laceration and uterine rupture were examined. The time between delivery and hysterectomy ranged from 15 min to 456 h. The specimens were stained with hematoxylin-eosin, elastica-van Gieson and an antioxytocin receptor antibody.

Changes in the uterine vessels varied substantially based on their location. The intima in arteries of the endometrial side thickened within 5 h after delivery. On the serosal side, phlebosclerosis was demonstrated 6 weeks postpartum. Immunoreactivity for the oxytocin receptor (OTR) appeared in the muscular medias of arteries 5 h after delivery although it was not expressed before this period.

Remodeling of uterine vessels involved thickening of the arterial intima and OTR expression in vessel walls during the first 5 h postpartum; the parameters normalized within 6 weeks. However, phlebosclerosis persisted for a long time on the serosal side.