1. The effect of repeated intravenous injections of frusemide (0.17 mg/kg) on the urinary kallikrein excretion of normal, adrenalectomized and deoxycorticosterone acetate (D0CA)-treated adrenalectomized rats was studied.
2. Adrenalectomy decreased baseline urinary kallikrein excretion, while DOCA treatment restored it to normal.
3. Frusemide injections repeatedly increased urinary kallikrein excretion in the three groups of rats studied. Compared with control and DOCA-treated animals, adrenalectomized rats were less responsive.
4. The excretion of urinary kallikrein was positively correlated with urine volume and with the excretion of sodium and potassium in all groups. The regression lines were shifted to the left in DOCA-treated adrenalectomized rats showing that mineralocorticoids enhance the effect of frusemide on urinary kallikrein excretion. The regression lines between urinary kallikrein excretion and the measured variables in adrenalectomized rats did not differ from those of control animals.
5. We conclude that the response of urinary kallikrein to frusemide is influenced by the level of mineralocorticoid activity. The effect of frusemide on urinary kallikrein excretion does not appear to be a ‘wash-out’ of the enzyme since its influence did not subside after repeated injections.