Renin, antidiuretic hormone and the kidney in water restriction and rehydration.

1. The effect of restricted water intake followed by voluntary rehydration with water or 10 mM-KCl was studied in four conscious sheep with respect to plasma concentrations of renin, antidiuretic hormone (ADH), protein and electrolytes, and urine flow rate, osmolality and osmolal excretion. 2. Water restriction increased the plasma renin concentration and the plasma ADH concentration. 3. Rehydration with water caused a further rise in plasma renin, but plasma ADH returned to basal levels in less than 2 hr. 4. Rehydration with 10 mM-KCl in order to stabilize plasma K concentration greatly attenuated the post-drinking rise in plasma renin concentration, while plasma ADH levels fell as before. 5. Urine flow rates after rehydration with water and 10 mM-KCl remained low for at least 6 hr in most experiments despite low plasma ADH levels. The effect on urine osmolality ranged from no change to a large drop. 6. The post-drinking antidiuresis was associated with a reduction in solute excretion rate. However, free water clearance usually remained negative. 7. These experiments do not support the existence of a direct nexus between plasma ADH levels and plasma renin concentration.