Hypothalamic & Pituitary Drugs

Introduction & the hypothalamic-pituitary axis

• Scope — Metabolism, growth and reproduction are controlled by an integrated hypothalamic-pituitary neuroendocrine unit; drugs in this class either replace a deficient hormone, antagonise an over-produced one, or are used for diagnostic testing.
• Two lobes — Anterior pituitary (adenohypophysis) — secretes GH, prolactin, TSH, ACTH, LH & FSH under hypothalamic releasing/inhibiting hormones delivered by the hypothalamic-adenohypophyseal portal system. Posterior pituitary (neurohypophysis) — not a true gland but axon terminals of magnocellular SON/PVN neurons storing & releasing oxytocin and vasopressin (AVP/ADH).
• Axis architecture — hypothalamic releasing hormone → amplified by an anterior-pituitary trophic hormone → target-endocrine-organ response → target hormone exerts negative feedback on both hypothalamus and pituitary.
• Clinically important drug groups — GH & GH-antagonists, somatostatin analogues, dopamine agonists, gonadotropins, GnRH (and analogues), oxytocin, and vasopressin/desmopressin — most pure hypothalamic peptides (TRH, CRH, GHRH) are used only diagnostically because the downstream target hormone is easier to give.