The relationship between kallikrein and water excretion and the conditional relationship between kallikrein and sodium excretion.

1. The renal kallikrein-kinin system has previously been linked with renal control of sodium and water excretion. The present investigations were carried out to examine more closely these relationships. 2. In physiological studies with rabbits, urinary kallikrein was measured by a modification of the [3-H]TAME method. 3. With rabbits on free sodium and water intake, urinary kallikrein was positively correlated with both sodium and water excretion. Kallikrein excretion was also negatively correlated with urinary osmolality. 4. In rabbits on chronic high and low sodium diets, urinary kallikrein was positively correlated with urinary volume but not with sodium excretion. 5. In rabbits held to a constant fluid intake but with sodium intake changed, urinary kallikrein was not correlated with sodium excretion. 6. These results indicate that the positive correlation of kallikrein excretion with sodium excretion under conditions of free sodium and water intake may be only secondary to the positive relationship of kallikrein excretion with urinary volume. 7. The results of the present investigations do not support the hypothesis that the renal kallikrein-kinin system is necessarily involved in renal control of sodium excretion under normal conditions but it is where a change in sodium intake leads to a change in fluid intake and consequently of urinary volume. 8. In the above experiments, urinary kallikrein was always positively correlated with urinary volume and negatively correlated with urinary osmolality. This may indicate a functional relationship between renal kallikrein and water excretion.