RU-486: The abortion pill explained

Staff Reports
California (U-Wire)

BERKELEY, Calif. (U-WIRE) - After years of controversy, the Food and Drug Administration last week approved the use of RU-486, also known as the abortion pill. Distribution of RU-486 in the United States is expected to begin within one month.

RU-486 was invented in France two decades ago and has been used for years to induce abortion in women in many European countries. When RU-486 acts on a woman's body after the fertilized egg has implanted into the uterus, the embryo is aborted. Use of the abortion pill has sparked controversy because of divided moral stances on the issue of abortion.

"RU" stands for Roussel-Uclaf, which is the name of the pharmaceutical company that produces the drug. "486" comes from the serial of the chemical substance called mifepristone found in the drug.

Upon entering the female body, RU-486 binds itself to progesterone receptors on the wall of the uterus and blocks the effect of the woman's natural progesterone. The inhibition of progesterone triggers the shedding of the uterine wall, much like a normal menstruation.

Progesterone is the hormone of pregnancy and its normal function is to quiet down the uterine muscle and increase the supply of blood so that sloughing of the endometrium lining of the uterus does not occur. Progesterone is a steroid hormone secreted by the ovary to stimulate changes in the endometrium of the uterus in preparation for the implantation of a fertilized egg. The relaxed state of the muscle and the thick blood lining provides a comfortable environment for an embryo to implant and grow.

During pregnancy, the progesterone hormone is produced in the placenta in large quantities to maintain the proper environment for the embryo to grow. Progesterone inhibits the synthesis of prostaglandins, which are hormones that induce uterine contraction. By inhibiting this activity, uterine contraction decreases and a new follicle is not released.

Low levels of progesterone just before a woman's period stimulate the sloughing of the uterine endometrium during menstruation in the case of no pregnancy.

Hormones such as progesterone have to be bound to their receptors on the uterine cells, where the hormone wants to exert its action to carry out its function.

RU-486 is an antiprogestin that acts by competitive binding with the progesterone receptors on the uterine wall. Because RU-486 competitively binds better than progesterone does to the receptor, progesterone is then not able to bind to its own receptor when it reaches the membrane of the uterine cells. RU-486 acts as an antagonist to progesterone and in doing so actually blocks the action of progesterone. Molecules that mimic the action of a natural molecule are called agonists; those that oppose it are antagonists.

The consequences of this inhibited binding is that when progesterone receptors are bound by RU-486, which has no progesterone action, the action of progesterone will not take place. With low levels of progesterone, the proteins necessary to begin and maintain pregnancy are not synthesized. The uterine mucosa is then under the influence only of estrogens. In the absence of this progesterone and the action of estrogen only, abortion will occur.

If RU-486 is taken shortly after intercourse, it prevents pregnancy because the contracting uterine muscles present a hostile environment unfavorable to implantation. If taken early in pregnancy, RU-486 induces contractions that destroy the quiet environment in the uterus and thus cause the embryo to be aborted. If implantation has occurred, there will be an abortion of the implanted fertilized egg.

RU-486 also opens the cervix and causes mild contractions, which help expel the embryo. The initial dose often causes some nausea, headache, weakness, diarrhea and fatigue. RU-486 is designed to be taken up to seven weeks after a woman misses her first period as prescribed by a doctor. After seven weeks, side effects are amplified. After one or two days, the woman has to go back to the clinic to take a prostaglandin pill, which causes her cervix to soften and dilate and contractions of the uterus to begin..