| • Science | • People | • Locations | • Timeline |
The normal function of ADH is to control the concentration of solutes--particularly sodium--in the blood. ADH acts in the distal portion of the renal tubule and causes the retention of water, but not solute. Hence, ADH activity promotes the dilution of sodium in the blood. It furthermore activates the brain's thirst mechanism, causing the individual to drink.
Through an unknown mechanism, CNS injury can cause the plasma ADH level to increase such that water is inappropriately retained by the kidneys. This retention leads to a dilutional hyponatremia and all the consequences associated with that condition: cerebral edema, increased intracranial pressure, hypertension, hyper-reflexia, and renal failure. Though commonly associated with CNS injury, SIADH can also result from an ADH-secreting tumor (usually small cell carcinoma of the lung ).
Treatment of SIADH includes fluid restriction and administration of isotonic saline.