1. The effect of amiloride administration on the urinary kallikrein response to the injection or continuous infusion of frusemide in normal Sprague–Dawley rats was investigated.
2. Injections of frusemide induced repeatedly an increase in urinary kallikrein excretion. This effect was suppressed by amiloride. Amiloride also blocked the response to mannitol injection. A continuous infusion of frusemide lasting 100 min also induced an increase in urinary kallikrein excretion which persisted throughout the experiment. This response was completely blocked by the injection of amiloride.
3. Urinary kallikrein excretion was directly and positively related to urine volume and urinary sodium excretion before and after amiloride injection. The regression lines had markedly decreased slopes after amiloride administration. The urinary kallikrein excretion was also positively related to the urine volume and urinary sodium excretion when frusemide was continuously infused. However, these relationships were abolished after amiloride injection.
4. In both the injection and the infusion experiments, there was a direct relationship of urinary kallikrein excretion to urinary potassium excretion. Although this relationship persisted after amiloride injection, the regression line was shifted to the left.
5. The suppression of the kallikrein stimulating effect of frusemide by the sodium channel blocker amiloride indicates that distal tubule sodium re-absorption is the triggering factor in urinary kallikrein excretion. The study suggests that the mechanism involved in the release of kallikrein by the distal tubular cells is linked to the renal mechanism affected by amiloride.