INTERRUPTION OF PREGNANCY IN THE RAT BY A UTERINE SUTURE

Abstract

A silk suture inserted into the uterine lumen prevented implantation in the rat. Normal embryos were present in the oviduct until Day 4 of pregnancy but were missing from the tract by Day 5. If the threaded uterus was ligated at the cervix at Day 4, degenerating ova were recovered the next day. This indicates that shortly after the ova entered the uterus they were usually expelled per vaginam. A leucocytic infiltration of the endometrium was consistently observed in cornua from which embryos were missing. The inflammatory reaction was accentuated by anti-inflammatory compounds which stimulated myelopoiesis. Two months after thread insertion, the uterus showed the histologic modifications associated with a chronic inflammation, i.e. a proliferative rather than a marked exudative response. The inflammatory reaction appeared to be essential for interruption of pregnancy since the absence of leucocytes was always correlated with implantation in the sutured cornu. The location of the thread determined whether a leucocytic reaction occurred. Implantation took place in the treated cornu if the thread had not penetrated into the lumen but instead was lodged in the stroma. This accounted for the presence of embryos in some of the threaded uteri despite the in situ location of the suture. Pregnancy continued when the thread was deliberately placed in the stroma, at some distance from the lumen.