Hemodynamic and natriuretic effects of bumetanide and furosemide in the cat

Renal hemodynamic and natriuretic effects of bumetanide and furosemide were studied by clearance and micropuncture methods in cats. Furosemide (0.04-5.0 mg/kg i.v.) effects increased with increasing doses up to a maximal fractional sodium (FEna) and water (V/GFR) excretion of 23%. GFR and superficial single nephron GFR remained constant. Renal blood flow (RBF) increased up to 45% over control. A preferential increase in outer cortical RBF occurred at 5.0 mg/kg. Bumetanide (0.001-0.14 mg/kg i.v.) raised FEna and V/GFR maximally by 26%. Only at a supramaximal dose (0.69 mg/kg) did bumetanide raise RBF and depress filtration fraction. Probenecid (50 mg/kg i.v.) failed to block the natriuretic effect of bumetanide (0.025 microgram/kg-min) when infused into one renal artery but abolished the natriuretic action of furosemide (1.0 microgram/kg-min). Probenecid failed to displace the dose-response curve for bumetanide.