Hypothalamic and Pituitary Hormones

Hypothalamic-Pituitary Axis - Brain's Hormone HQ

The hypothalamus (control center) and pituitary gland (master gland) form a crucial neuroendocrine link, regulating many bodily functions.

• Hypothalamus:
  • Releasing Hormones (RH): e.g., GnRH (Gonadotropin-Releasing Hormone), CRH (Corticotropin-Releasing Hormone), TRH (Thyrotropin-Releasing Hormone), GHRH (Growth Hormone-Releasing Hormone).
  • Inhibiting Hormones (IH): e.g., Somatostatin (Growth Hormone-Inhibiting Hormone, GHIH), Dopamine (Prolactin-Inhibiting Hormone, PIH).
• Pituitary Gland:
  • Anterior Lobe (Adenohypophysis): Secretes tropic hormones.
    • 📌 Mnemonic: FLAT PEG (FSH, LH, ACTH, TSH, Prolactin, Endorphins, GH).
  • Posterior Lobe (Neurohypophysis): Stores & releases hypothalamic hormones (Oxytocin, ADH/Vasopressin).
• Feedback Loops:
  • Negative Feedback: Predominant mechanism; ↑hormone levels inhibit further hypothalamic/pituitary release.
  • Positive Feedback: Rare; e.g., oxytocin during labor, estrogen surge pre-ovulation.

⭐ Negative feedback is the predominant mechanism controlling hormone secretion in the hypothalamic-pituitary system.

Anterior Pituitary Hormones (I) - Growth & Gonad Gurus

• Growth Hormone (GH) Axis:
  • Agonists:
    • Somatropin (rhGH): GH deficiency, Turner's. SE: edema, arthralgia.
    • Mecasermin (rhIGF-1): IGF-1 def. (Laron dwarfism). SE: hypoglycemia.
  • Antagonists:
    • Pegvisomant (GH-R antag): Acromegaly. SE: ↑LFTs.
    • Octreotide, Lanreotide (Somatostatin analogs): Acromegaly, carcinoid. SE: GI upset, gallstones.
• Prolactin (PRL) Axis:
  • Antagonists (Dopamine D2 Agonists): Bromocriptine, Cabergoline.
    • Uses: Hyperprolactinemia, acromegaly (adjunct). SE: nausea, postural hypotension.
• Gonadotropin (FSH, LH) & GnRH Axis:
  • Gonadotropins: Menotropins (FSH+LH), Follitropin (rFSH), hCG (LH-like).
    • Uses: Infertility (ovulation induction). SE: Ovarian Hyperstimulation Syndrome (OHSS), multiple pregnancies.
  • GnRH Agonists: Leuprolide, Goserelin.
    • Pulsatile: Infertility. Continuous: Prostate Ca, endometriosis, fibroids. SE: initial flare, menopausal sx, osteoporosis (long-term).
    • 📌 Leuprolide: Continuous use → paradoxical suppression.
  • GnRH Antagonists: Ganirelix, Cetrorelix, Degarelix.
    • Uses: IVF (prevent LH surge), Prostate Ca. SE: site rxns.

⭐ Continuous administration of GnRH agonists like Leuprolide paradoxically suppresses gonadotropin release, a principle used in treating hormone-sensitive cancers.

Anterior Pituitary Hormones (II) & Posterior Hormones - Stress, Water, & Uterine Wizards

Anterior Pituitary Diagnostic Agents:

• Cosyntropin (ACTH analogue): Diagnoses adrenal insufficiency.
• Thyrotropin alfa (TSH analogue): Diagnostic in thyroid cancer management (post-thyroidectomy).

Posterior Pituitary Hormones & Analogues/Antagonists:

Desmopressin is preferred over vasopressin for treating central diabetes insipidus due to its longer duration of action and greater V2 receptor selectivity, minimizing pressor effects.

📌 Vaptans for Volume And Pressure To Abate Na+ Status (used in SIADH).

High‑Yield Points - ⚡ Biggest Takeaways

• Leuprolide (GnRH agonist): Initial flare, then suppression; treats prostate cancer, endometriosis.
• Octreotide (Somatostatin analogue): Manages acromegaly, carcinoid syndrome, variceal bleeding.
• Bromocriptine/Cabergoline (Dopamine agonists): First-line for hyperprolactinemia.
• Desmopressin (ADH analogue): Treats central DI, nocturnal enuresis, von Willebrand Disease (vWD).
• Oxytocin: Induces labor; risk of uterine hyperstimulation, fetal distress.
• Pegvisomant: GH receptor antagonist for acromegaly unresponsive to somatostatin analogues.
• Conivaptan/Tolvaptan: ADH antagonists for SIADH (Syndrome of Inappropriate ADH secretion).