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Questions and Answers
What is the primary mechanism of action of antiprogestins like Mifepristone?
In what way do antiprogestins like Mifepristone prevent ovulation?
Apart from termination of early pregnancy, for what other purpose can Mifepristone be used?
What effect does the antiglucocorticoid action of Mifepristone provide in cases of in-operable Cushing’s syndrome?
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How does mifepristone prevent pregnancy?
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What is the main clinical use of mifepristone?
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Which enzyme is responsible for metabolizing mifepristone in the liver?
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What property of mifepristone contributes to its long duration of action?
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Why is natural endogenous progesterone not orally effective?
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How do synthetic progestins differ from natural endogenous progesterone?
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What is a characteristic of norethindrone among the synthetic progestins mentioned?
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What is the primary physiological action of progesterone in hormone replacement therapy?
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Study Notes
Mechanism of Action of Antiprogestins
- Antiprogestins like Mifepristone primarily act by blocking progesterone receptors, inhibiting progesterone's effects on the uterus.
- This blockade leads to the softening of the uterine lining and potential termination of early pregnancy.
Prevention of Ovulation
- Mifepristone prevents ovulation by disrupting the hormonal balance necessary for ovulation to occur.
- By inhibiting progesterone, it alters the luteal phase, preventing the release of the egg.
Additional Uses of Mifepristone
- Beyond terminating early pregnancy, Mifepristone is used in the management of conditions like Cushing's syndrome and facilitating medical abortion when combined with prostaglandins.
Antiglucocorticoid Action in Cushing's Syndrome
- Mifepristone’s antiglucocorticoid action interferes with cortisol effects, aiding in symptom management for inoperable Cushing's syndrome.
Mechanism of Preventing Pregnancy
- Mifepristone prevents pregnancy by blocking the progesterone that stabilizes the endometrium during the menstrual cycle, thus leading to the breakdown of the endometrial lining.
Main Clinical Use
- The foremost clinical application of Mifepristone is as an abortifacient in the medical termination of early pregnancy.
Metabolism of Mifepristone
- Mifepristone is metabolized in the liver primarily by the enzyme CYP3A4.
Duration of Action
- The long duration of action of Mifepristone is attributed to its strong affinity for progesterone receptors, allowing prolonged effects despite elimination.
Effectiveness of Natural Progesterone
- Natural endogenous progesterone is not orally effective due to significant first-pass metabolism in the liver, reducing its bioavailability.
Synthetic Progestins vs. Natural Progesterone
- Synthetic progestins are designed to resist metabolism and have modified structures that enhance their effectiveness compared to natural progesterone.
Characteristic of Norethindrone
- Norethindrone, a synthetic progestin, possesses properties that allow for extended half-life and increased resistance to breakdown, making it highly effective for contraception.
Physiological Action of Progesterone in Hormone Replacement Therapy
- In hormone replacement therapy, progesterone primarily maintains the uterine lining and reduces the risk of endometrial hyperplasia in women receiving estrogen.
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Description
Learn about antiprogestins, such as Mifepristone, onapristone, and gestione, and how they competitively inhibit progestin at progesterone receptors to prevent ovulation, fertilization, and implantation. Discover their role in delaying endometrial maturation and the appearance of the implantation window, especially in the context of termination of early pregnancy.
