Osmoreceptors controlling ADH (vasopressin) secretion are located primarily in which hypothalamic nucleus, and what is the osmolality threshold that triggers ADH release?

• A Anterior hypothalamic area; threshold ~295 mOsm/kg
• B Supraoptic and paraventricular nuclei; threshold ~280 mOsm/kg ✓
• C Arcuate nucleus; threshold ~300 mOsm/kg
• D Suprachiasmatic nucleus; threshold ~270 mOsm/kg

Explanation

ADH is synthesised in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus. Dedicated osmoreceptors in the anterior hypothalamus (and adjacent organum vasculosum of the lamina terminalis, OVLT) sense plasma osmolality; the osmotic threshold for ADH release is approximately 280 mOsm/kg. Below this threshold, essentially no ADH is secreted, allowing free water excretion. ADH release rises steeply above this threshold, increasing water reabsorption in the collecting duct. Options B–D have incorrect nuclei or thresholds.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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