Neuropeptide Y (NPY) can cause diuresis, natriuresis, and calciuresis in rats independently of the pressure-natriuresis mechanism (A. Bischoff and M. C. Michel. Pflügers Arch. 435: 443-453, 1998). Because this is seen in systemic but not intrarenal NPY infusion, we have investigated the possible mediator of tubular NPY effects in anesthetized rats. In the present study, infusion of NPY (2 µg · kg¹ · min¹) enhanced renovascular resistance by 8 mmHg · ml¹ · min and enhanced urine and sodium excretion by 450 µl/15 min and 60-85 µmol/15 min, respectively. Acute renal denervation did not alter renovascular or tubular NPY effects, indicating that a neuronally released mediator is not involved. Treatment with the angiotensin II-receptor antagonist losartan prevented the decline of the renovascular response with time but did not modify tubular NPY effects. The bradykinin B₂-receptor antagonist icatibant accelerated the decline of the renovascular NPY effects with time; concomitantly, it attenuated NPY-induced diuresis and natriuresis and abolished NPY-induced calciuresis. The converting-enzyme inhibitor ramiprilat prevented the decline of the renovascular response with time; concomitantly, it magnified the NPY-induced diuresis, natriuresis, and calciuresis. We conclude that bradykinin may be involved in NPY-induced diuresis, natriuresis, and, in particular, calciuresis.