Uremic levels of BUN do not cause nitric oxide deficiency in rats with normal renal function

In vitro, 7 days of high blood urea nitrogen (BUN) inhibits endothelial L-a rginine transport and nitric oxide synthase (NOS) activity. The present stu dy investigates whether 7 days of high BUN in vivo influences renal hemodyn amics, blood pressure (BP), and/or the nitric oxide (NO) system. Normal rat s were fed low-nitrate food containing 30% urea for 7 days, which increased BUN (15 +/- 1 to 69 +/- 4 mg/100 ml, P< 0.001). High BUN did not reduce 24 -hour urinary nitrite/nitrate excretion (a measure of total NO production). Baseline BP and renal hemodynamics were unaffected by high BUN as were the pressor and renal vasoconstrictor responses to acute NOS inhibition with N -G-nitro-L-arginine-methyl ester. In addition, high BUN had no impact on re nal cortical L-arginine concentration, density of either endothelial NOS or neuronal NOS protein, or renal cortical NOS activity. NOS activity in the brain cerebellum was also unaffected. In conclusion, high BUN did not lead to vasoconstriction or NO deficiency in rats with normal renal function. Fu rther studies are needed to evaluate the effect of high BUN on the NO syste m in rats with progressive renal functional insufficiency.