Estrogens and Progestins

Introduction & definitions

• Estrogens — the female sex hormones that induce estrus in ovariectomized animals — responsible for pubertal development, cyclical preparation of the reproductive tract, and actions on bone, lipid, carbohydrate and coagulation systems. Prototype: 17β-estradiol.
• Progestins — compounds with progesterone-like activity ("favouring pregnancy") that convert an estrogen-primed proliferative endometrium to secretory and maintain pregnancy. Natural hormone: progesterone; synthetic agents are termed progestins/progestagens/gestagens.
• Common mechanism — both act via nuclear receptors (ligand-activated transcription factors); estrogen also has partly unliganded and rapid membrane (nongenomic) actions.
• Two dominant clinical settings — contraception and menopausal hormone therapy (MHT/HRT) — agents and doses differ greatly (combined pills use 20–35 µg/day ethinylestradiol; MHT uses conjugated estrogens ≈0.625 mg/day).
• Receptor-modifying drugs — antiestrogens (clomiphene) treat anovulatory infertility; antiprogestins / progesterone-receptor modulators (mifepristone, ulipristal) are used for medical abortion and emergency contraception.