Effects of postcoital insertion of an intrauterine foreign body in rats

Abstract

The effects of brief exposure to an intrauterine foreign body (IUFB) were studied in pregnant and pseudopregnant rats. Insertion of an IUFB on the morning of day 1 or 2 of pregnancy (day 1 = day of vaginal sperms) and its removal about twenty-four hours later did not influence implantation or decidual growth. However, exposure during days 3–4 inhibited both implantation and deciduomal change. Exposure of upper (ovarian) or lower (cervical) half of the uterus during days 3–4 or the sham procedure of IUFB insertion itself did not prevent implantation but it caused high embryo mortality. Exposure during days 4–5 did not prevent decidual change but it inhibited both implantation and decidual growth. Other studies indicated that exposure during days 3–4 caused: (1) a significant increase in the number of leucocytes in the uterine lumen; (2) stimulated mitosis in the luminal epithelium; (3) advanced from pseudopregnancy day 5 to day 4 the peak in uterine weight and nuclear DNA-dependent RNA polymerase activity; and (4) significantly inhibited uterine weight, RNA and DNA-dependent RNA polymerase response to a decidualizing stimulus. These studies demonstrate that an IUFB can act as an effective postconceptional type of contraceptive in rats. Furthermore, it is suggested that the antifertility effect of an IUFB insertion on day 3 may be mainly due to partial inhibition of uterine responses to ovarian hormones and that of an insertion on day 4 may be mainly due to an inhibitory influence of decidual change on implantation.