Mechanism of action of intrauterine devices: biochemical changes.

The mechanism of action of intrauterine devices varies from one type of device to another, although the principle of action is the same, namely, to interfere with the physiology of reproduction at the endometrial level. The biochemical changes of the endometrial tissue and the composition of the uterine fluid have been reviewed in relation to the use of inert, copper-medicated and steroid-releasing IUDs. All IUDs, whether inert or medicated, provoke a significant increase in the number of neutrophils, mononuclear cells and plasma cells, the presence of which is unrelated to the tissue infiltration of inflammatory cells occurring pre-menstrually of the normal menstrual cycle. The increase of leucocytes in IUD-users is compatible with a foreign body reaction which may be related to the antifertility effect. The addition of copper to an inert IUD has been shown to significantly alter the metabolism of the endometrial cells, e.g. the enzymatic activity and the DOVA-synthesis. The steroid-medicated IUDs represent a new approach to intrauterine contraception where the morphology of the endometrium is considerably altered, showing massive decidual changes, atrophic glands and sometimes atrophy of the whole functional layer. In addition, there is an important foreign body reaction, similar to that of the inert IUDs. The enzymatic activity, as well as the proliferative activity was significantly altered in the endometrium of these IUD-users. Changes in the endometrial fibrinolytic activity in IUD-users have been demonstrated to be related to the presence of irregular bleeding. Micro-traumata of the endometrium and the increased fibrinolytic activity may also interfere with the protective processes present in the physiologically normal endometrium. Further studies on the factors influencing the fertilizing ability of the spermatozoa in the female genital tract, as well as on the conditions of the human endometrium required for the implantation of a blastocyst, may yield important information for the improvement of intrauterine contraception.