Dubbed the "French abortion pill" and the "month after pill", the pharmaceutical RU-486 was released to wide acceptance in Europe in 1988, but was delayed for licensing in the United States by the Food and Drug Administration until September 2000, because of political pressure against abortions. In France, where the drug was developed, about one-third of all abortions are performed using the synthetic steroidal hormone.

Known to doctors as mifepristone and to pharmacists by the trade name Mifeprex, RU-486 is a synthesized prostaglandin that interferes with progesterone metabolism. By making the uterine lining inhospitable to the developing embryo, the zygote fails to attach, is deprived of nutrients, and is miscarried. Administered as a three-tablet regimen, a mifepristone dose is taken first, followed two days later by two misoprostol tablets, the latter causing contractions and expulsion of the uterus' contents. As an at-home option and alternative to surgery, RU-486 provides a private procedure for terminating an early pregnancy. It can also function as a "morning-after pill" and as a menstrual initiator.

Originally named RU 38486 by French pharmaceutical company Roussel-Uclaf (thus "RU"), mifepristone forms a yellow powder with a molecular weight of 429.6, a melting point of 191 to 196 degrees Celsius, and is insoluble in water or hexane and very soluble in methanol, chloroform, and acetone. RU-486 acts as an antagonist for progesterone by binding to the progesterone site, tying itself to the hormone, and blocking its release. Mifepristone is a substituted 19-nor steroid compound designated by organic chemists as 11beta-[p-(Dimethylamino)phenyl]-17beta-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one.

RU-486 Time Lapse Sequence #1 - Fan-like edges of large, growing spherulites advance into the viewfield in this time-lapse sequence of 26 images.

RU-486 Time Lapse Sequence #2 - A 30-image time-lapse sequence illustrates the merging edges of several large spherulites.

RU-486 Time Lapse Sequence #3 - As spherulites form and grow in size within the viewfield they intersect the edges of even-larger crystallites as they enter the field from the margins in a sequence of 35 images.

RU-486 Time Lapse Sequence #4 - The growth of a number of spherulitic crystallites is illustrated in a time-lapse sequence of 38 images.

RU-486 Time Lapse Sequence #5 - This sequence of 38 time-lapse images displays birefringence of a beautiful uniform blue that gives the growing spherulites a metallic appearance.

RU-486 Time Lapse Sequence #6 - In this 20-image sequence, several spherulites grow in size followed by the filling of the space between them with crystalline material that appears to be deformed or incomplete fragments.

RU-486 Time Lapse Sequence #7 - A time-lapse sequence of 27 images illustrates the growth of spherulites.

RU-486 Time Lapse Sequence #8 - Intersecting spherulites grow into a confluent field in a sequence of 26 images.

RU-486 Time Lapse Sequence #9 - A 33-image time-lapse sequence illustrates crystallizing spherulites as they advance toward the center of the viewfield from the margins.

RU-486 Time Lapse Sequence #10 - This 23-image sequence illustrates the converging growth of spherulites of a variety of sizes.

RU-486 Time Lapse Sequence #11 - A time-lapse sequence of 49 images shows the formation of several complete spherulites followed by the appearance of regions of apparently-deformed or fragmented material.

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