ADH

• Antidiuretic hormone (ADH)


  Also called vasopressin, it is secreted by the posterior pituitary gland
• Neurons that synthesize ADH


  • Located in the supraoptic nucleus of the hypothalamus
• Stimuli for ADH secretion

  • Low blood pressure
  • High plasma osmolality
• Osmoreceptors

  Detect changes in blood osmolality and stimulate ADH release
• Angiotensin II


  Hormone that binds to receptors in the hypothalamus and stimulates ADH release in response to low blood pressure
• Principle cell

  • Located in the collecting duct of the nephron, has receptors for ADH
• ADH mechanism of action


  1. Binds to V2 receptors on principle cells

  2. Activates G-protein

  3. Activates adenylate cyclase

  4. Increases cAMP

  5. Activates protein kinase A

  6. Stimulates transcription and translation of aquaporin-2

  7. Inserts aquaporin-2 channels into apical membrane
• Aquaporin-2

  Water channel protein inserted into apical membrane of principle cells in response to ADH, allowing water reabsorption
• Aquaporin-3 and 4

  Water channel proteins constitutively expressed on the basolateral membrane of principle cells, allowing water movement out of the cell
• Normally, water flows through the nephron and is excreted as urine, but ADH allows water reabsorption by inserting aquaporin-2 channels
• Aquaporins

  Proteins located on the basolateral membrane that are always open
• Aquaporin 3 & 4

  The specific aquaporins located on the basolateral membrane that are always open
• ADH is present

  Aquaporin channels are made
• Water is a very integral component of urine
• Protein kinase A stimulation

  1. Phosphorylation reactions

  2. Protein migration and fusion with cell membrane
• Aquaporins

  • Open up to allow water to flow into the cell
  • Allow water to then flow out of the cell into the blood
• Increased water in blood

  • Increases plasma volume
  • Increases blood pressure
• Increased water in blood

  Decreases plasma osmolality towards isotonicity
• Vasopressin (ADH) type 1 receptor

  Receptor on blood vessel smooth muscle cells that binds ADH and causes vasoconstriction
• Vasopressin (ADH) binding to type 1 receptor

  • Increases calcium in smooth muscle cells
  • Causes vasoconstriction
  • Increases peripheral resistance
  • Increases blood pressure
• Diabetes insipidus

  Condition of low ADH secretion, usually due to hypothalamus/pituitary damage, leading to polyuria and polydipsia
• Syndrome of inappropriate ADH secretion

  Condition of excessive ADH secretion, leading to water retention, decreased solute concentration, and cerebral edema