WBR0510
| Author | [[PageAuthor::Gonzalo A. Romero, M.D. [1] (Reviewed by Will Gibson)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pharmacology, MainCategory::Physiology |
| Sub Category | SubCategory::Endocrine, SubCategory::Reproductive |
| Prompt | [[Prompt::A pharmacist is planning a study with mice in order to determine the effects of a novel drug called “Compound A572”. He knows that the drug is supposed to work in the hypothalamus, to regulate the release of different pituitary hormones. He measures serum concentration of hypothalamic hormones and determines that the drug causes different changes in FSH and LH if dosed continuously or in a pulsatile fashion. Which of the following drugs has a similar mechanism of action as “Compound A572”?]] |
| Answer A | AnswerA::Flutamide |
| Answer A Explanation | [[AnswerAExp::Flutamide is a nonsteroidal competitive inhibitor of androgens at the androgen receptor. It is used to treat prostate cancer and hyperandrogenism in polycystic ovarian syndrome.]] |
| Answer B | AnswerB::Finasteride |
| Answer B Explanation | [[AnswerBExp::Finasteride is a 5 alpha-reductase inhibitor used to treat benign prostatic hyperplasia and male-pattern baldness.]] |
| Answer C | AnswerC::Mifepristone |
| Answer C Explanation | [[AnswerCExp::Mifepristone is a competitive inhibitor of progestins at the progesterone receptors. It is used to terminate pregnancy in combination with misoprostol (PGE1 analogue).]] |
| Answer D | AnswerD::Ketoconazole |
| Answer D Explanation | [[AnswerDExp::Ketoconazole is a steroid synthesis inhibitor that inhibits desmolase, the enzyme responsible for transforming cholesterol into pregnenolone.]] |
| Answer E | AnswerE::Leuprolide |
| Answer E Explanation | [[AnswerEExp::Leuprolide is a GnRH analogue. When dosed continuously, it inhibits the production of FSH and LH, thereby leading to hypogonadism. When dosed in a pulsatile manner, it increases the production of FSH and LH. In turn, FSH and LH stimulate the production of sex hormones.]] |
| Right Answer | RightAnswer::E |
| Explanation | [[Explanation:: Leuprolide is a GnRH analogue. GnRH is normally secreted in a pulsatile fashion to stimulate the HPA axis. GnRH secretion is negatively regulated by prolactin secreted in the pituitary. GnRH is thought to be positively regulated by kisspeptin, but the precise circuitry underlying the GnRH pulse generator is still unclear. Leuprolide acts similarly to endogenous GnRH; when used in pulsatile fashion, it acts as an agonist, while if used continuously, it acts as an antagonist. Continuous dosing of the drug causes the pituitary to downregulate GnRH receptors due to negative feedback. The anterior pituitary thereby decreases the production of Follice Stimulating Hormone (FSH) and Leutenizing Hormone (LH). Recall that FSH and LH are responsible for stimulating the release of sex hormones in both men and women. Leuprolide therefore causes hypogonadism and has important therapeutic roles in diseases associated with the activity of sex hormones. Leuprolide is often used continuously with flutamide to treat prostatic cancer or uterine fibroids. Leuprolide is administered in pulsatile dosing in cases of infertility. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Pituitary hormones, WBRKeyword::Pituitary, WBRKeyword::Hypothalamus, WBRKeyword::GnRH, WBRKeyword::Gonadotropins, WBRKeyword::Gonadotropin releasing hormone, WBRKeyword::Gonadotropin, WBRKeyword::Leuprolide, WBRKeyword::Hormone |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |