Nitric oxide and renal effects of volume expansion in conscious monkeys

Experiments were performed to determine the effects of nitric oxide (NO) synthase inhibition on the renal responses to volume expansion in conscious cynomolgus monkeys. All animals were volume expanded with 3% dextran in normal saline under three conditions: 1) during a control state, 2) during constant infusion of the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 30 microg x kg(-1) x min(-1)), and 3) during simultaneous infusion of L-NAME and excess NO substrate L-arginine (0.6 mg x kg(-1) x min(-1)). The control volume expansion increased urine flow from 0.27 +/- 0.05 to 0.94 +/- 0.28 ml/min and sodium excretion from 21 +/- 9 to 95 +/- 26 microeq/min. During L-NAME infusion, these responses were attenuated in that urine flow only increased from 0.13 +/- 0.03 to 0.28 +/- 0.09 ml/min and sodium excretion from 13 +/- 8 to 35 +/- 23 microeq/min. Addition of L-arginine to the L-NAME infusion abolished these renal excretory effects of L-NAME alone. With combined L-NAME/L-arginine, volume expansion increased urine flow from 0.37 +/- 0.23 to 1.09 +/- 0.23 ml/min and sodium excretion from 38 +/- 27 to 150 +/- 24 microeq/min, responses similar to control. L-Arginine also markedly attenuated the effect of L-NAME to increase mean arterial pressure and abolished the L-NAME decreases in creatinine and p-aminohippurate clearances. However, an L-NAME-induced bradycardia could only be partially reversed. These results demonstrate that a functioning NO system may be important in mediating normal renal responses to volume expansion in this primate species.