Ultrastructure of Human Uterine Epithelium at the Time of Implantation after Postovulatory Administration of Norethindrone

Abstract

The present investigation was performed to elucidate the mechanism of action of the previously demonstrated contraceptive effect in women of postovulatory administration of a synthetic gestagen, norethindrone (NET). Seven women participated during 3 control cycles and during 8 treatment cycles, in which NET was given orally after ovulation. Daily peripheral plasma levels of progesterone, estradiol and NET were assayed. An endometrial biopsy was taken in all cycles at about the expected time of implantation. Light microscopy revealed no consistent differences between non-treatment and treatment cycles but electron microscopy indicated that, after NET treatment, the mitochondria had grown larger and that nucleolar channel system had appeared. These changes suggest an increased progesterone-like influence upon the epithelium, despite the decreased progesterone plasma levels, caused by NET. It is assumed that these structural changes, caused by the postovulatory NET treatment, might change the functional properties of the endometrium and thereby impair the possibilities for normal implantation.