1. To establish whether or not vasoactive intestinal peptide (VIP) acts directly on the kidney and also to define the renal responses to it, we compared the natriuretic and haemodynamic responses to VIP (10−4–100 pmol min−1 kg−1) infused intravenously with those obtained by direct infusion into the renal artery in seven conscious male rabbits.

2. VIP had significant effects on the renal circulation without changing systemic arterial pressure or pulse rate. There was a significant fall from control in effective renal plasma flow (P < 0.05 renal infusion, P < 0.01 intravenous infusion) and glomerular filtration rate (P < 0.01 renal, P < 0.05 intravenous). The derived renal vascular resistance rose significantly from control (P < 0.01 renal, P < 0.01 intravenous).

3. Despite the significant decline in filtered sodium load (P < 0.01 renal, P < 0.001 intravenous), there was a significant log dose-related increase in fractional sodium excretion (P < 0.005) with intrarenal infusion of VIP.

4. We conclude that the actions of VIP on intrarenal blood vessels and renal tubules are direct, leading to increases in renal vascular resistance and fractional sodium excretion.

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