alpha-Adrenergic (norepinephrine) effect on antidiuretic hormone activity.

The mechanism by which norepinephrine (NE) inhibits the antidiuretic activity of anti-diuretic hormone (ADH) was studied in anesthetized normal and ADH-deficient rats. NE infusion increased aortic blood pressure and resulted in increased urine volume and sodium and potassium excretion without changes in creatinine excretion. p-Aminohippuric acid excretion did not change in normals and rose (from 34 +/- 9 to 51 +/- 11, P less than 0.025) in ADH-deficient rats. Urine osmolality fell in normals (from 363 +/- 29 to 298 +/- 42, P less than 0.05) but not in ADH deficients (from 332 +/- 29 to 363 +/- 26, p less than 0.1). ADH-deficient rats given 50 muU per kg-min of ADH intravenously responded with antidiuresis, including hyperosmolality (from a range of 225 to 240 to a range of 332 to 333, P less than 0.025). When NE was infused at 0.5 mug per kg-min, no inhibition of hyperosmolality was noted but natriuresis and augmented volume excretion occurred. At 1.5 mug per kg-min, NE completely reversed the hyperosmolality induced with ADH. The results suggest that NE-induced pressure diuresis reduces osmolality only when ADH is present in the system and so by competitive inhibition of ADH action on the renal tubule.