1. Osmotic diuresis was induced in male Sprague-Dawley rats by a 30% (w/v) mannitol solution injected three times at 15-min intervals. Kallikrein excretion increased for a short period after the first two injections, but, despite marked diuresis, the increment of kallikrein excretion after the second injection was less marked than after the first and no enhanced kallikrein excretion was observed after the third injection of mannitol.
2. Urinary kallikrein excretion correlated only with urinary potassium excretion. No correlation was found with either urine volume or urinary sodium excretion.
3. At the end of the osmotic diuresis kallikrein activity was significantly reduced both in the urine and in the renal cortex. At that time plasma aldosterone concentration was slightly greater in the mannitol-treated than that in the control group, but the difference did not reach statistical significance.
4. In this experiment no relationship was observed between the activity of the renal kallikrein-kinin system and the plasma aldosterone concentration.
5. The transient increase in urinary kallikrein excretion is interpreted as a wash-out effect of renal kallikrein, which is followed by a diminished kallikrein activity in urine and in renal cortex.