Terminology

1. Official name: Vasopressin (because it raises blood pressure when present at high concentrations; in the physiological range of concentrations, its main action is on water permeability)

2. Abbreviated ADH (AntiDiuretic Hormone)

Synthesis and Release

1. Synthesized in the hypothalamic supraoptic and paraventricular nuclei (neurosecretory cells)

2. Migrate by axonal transport to nerve endings in the posterior pituitary (neurohypophysis) via the hypothalamo-hypophyseal tract

3. Stored in the posterior pituitary

4. Released into the posterior pituitary capillaries when the neurosecretory cells discharge (action potentials)

Transport and Action

1. Transported to all parts of the body by the circulation, but major action is in the kidney

2. Collecting duct action: binds to V2 receptors on Principal cells of the collecting duct, causing an increase in water permeability by inducing water channels (aquaporins) stored in intracellular vesicles to fuse with the luminal membrane (major effect)

Note: The effect on water permeability is graded -- the higher the ADH concentration, the more receptor sites occupied, and the greater the water permeability (up to the maximum effect)

Note: The other type of collecting duct cell is the Intercalated cell, which is important in acid-base balance

3. ADH also increases urea permeability of the collecting duct principal cells (supporting effect)

4. ADH has rapid action and rapid turnover (10-20 minutes)