Clinical case and answers 81

What leads to hyponatremia in adrenal crisis?

Pre renal state due to low cortisol	5 (26%)
CRH release leads to hyponatremia	2 (10%)
Cortisol normally suppresses ADH and in adrenal insuff, this doesn't happen	11 (57%)
The mechanism is not known	6 (31%)

The hypersecretion of ADH seen in low cortisol states may be due in part to the reductions in blood pressure and cardiac output. However, a more important mechanism may be that cortisol deficiency lead to increase CRH production leading to increase ADH state.  Cortisol feeds back negatively on CRH and ACTH, an inhibitory effect that is removed with adrenal insufficiency. In addition, cortisol appears to directly suppress ADH secretion. Thus, ADH levels increase when plasma cortisol levels are low.  Alternatively, the hypersecretion of ADH induced by aldosterone deficiency is caused by renal salt wasting with resultant volume depletion. Many studies support the concept that hyponatremia in patients with hypopituitarism is mainly caused by failing inhibition of ADH secretion because of hypocortisolism.

http://jasn.asnjournals.org/content/17/7/1820.long is an amazing reference from JASN that looks at water homeostasis in adrenal disorders.