Neuropeptide Y enhances potassium excretion by mechanisms distinct from those controlling sodium excretion

Neuropeptide Y (NPY) is an established modulator of renal function. Although NPY reduces renal blood flow and does not alter glomerular filtration rate, it enhances diuresis and natriuresis. Although initial studies on natriuresis did not detect kaliuresis, we now report that a retrospective analysis of previous studies regarding natriuresis demonstrates NPY-induced kaliuresis under several experimental conditions. Kaliuresis was observed despite a marked reduction in urinary potassium concentrations, which may explain why it has not been noted in some initial studies. In a direct comparison of NPY-induced kaliuresis and natriuresis, both effects were slow in onset (requiring >45 min to develop fully) and blocked by the cyclooxygenase inhibitor indomethacin. While natriuresis occurred solely via a Y5 receptor, kaliuresis involved a Y1 receptor and an additional receptor subtype, possibly Y2. The L-type Ca2+ entry blocker nifedipine abolished natriuresis but did not inhibit kaliuresis. A combination of experiments with the bradykinin B2 receptor antagonist icatibant, the angiotensin II receptor antagonist losartan, and the converting enzyme inhibitor ramiprilat revealed that NPY-induced natriuresis involves bradykinin while kaliuresis involves angiotensin II. We conclude that NPY-induced kaliuresis is much less pronounced than natriuresis and is mediated by distinct mechanisms.