The Thirst Axis
- ADH (/vasopressin) is synthesised in the hypothalamus.
- From there it migrates in neurosecretory granules along axonal pathways to the posterior pituitary gland.
- Secretion of ADH is principally in response to changes in plasma osmolality. It acts on the collecting duct of the kidney to cause water reabsorption via the translocation of aquaporin channels in the CD lumen, and is therefore stimulated when we need to conserve water volume. It is stimulated by large falls in blood pressure or volume.
- At high concentrations, ADH also causes vasoconstriction.
- ADH is suppressed at plasma osmolality <280mOsm/kg to permit maximal water diuresis.
- ADH secretion reaches a maximum at an osmolality of >296mOsm/kg.