ANTIPROGESTINS-DRUGS FOR ABORTION
As we have already seen that progestins such as progesterone are the agents aiding and maintaining pregnancy.Any drug which opposes or block the actions of progesterone will result in the termination of pregnancy or abortion.
Although anti estrogens have been available since the late 1950s the first report of an antiprogestin appear only after 1981.In that year a drug which is a glucocorticoid antagonist was reported by the name RU-38486 or simply RU-486 was having some anti gestagenic properties also.Later the drug was named as mifepristone.
Although mifepristone's main use is as a terminator of early pregnancy these anti progestins also are tried for the uses as contraceptives,anti cancer drugs,and agents to induce labour.
Chemistry Structurally mifepristone is related to progesterone as a seroidal compound.It is a derivative of norethindrone (a progestin with a methyl group at the 19 th position of its steroidal structure) with a dimethyl-aminophenyl substituent at the 11-b position.
Mechanism The mechanism of action of mifepristone is that because of its similarity in chemical structure to progesterone it competitively inhibit its receptors and block the pregnancy protecting effect of progesterone at the sensitive tissues like uterus, and thereby causes early contraction of the uterus and terminate the pregnancy.
But mifepristone when present alone in the absence of progesterone it will act as a weak progestin by acting as a partial agonist.
Mifepristone also act on the progesterone sensitive tissues of ovary.If given for a short period in the later follicular phase of the menstrual cycle,it delays ovulation by depressing LH surge.If it has been given frequently or continuously it can prevent ovulation but not in all cases.
If administered for several days in mid or late luteal phase mifepristone disturb the development of the secretory endometrium and causes menses.
Mifepristone is also having effects oncervix,myometrium,ectopic endometrial tissue,breast cancers,and meningiomas
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