INTRAVENOUS ADMINISTRATION OF L-ARGININE INHIBITS ANGIOTENSIN-CONVERTING ENZYME IN HUMANS

The iv administration of L-arginine, a precursor of endothelium-derive d relaxing factor/nitric oxide, is known to decrease blood pressure in humans by its direct vasodilatory effects. The purpose of the present study was to determine whether L-arginine infusion modifies the renin -angiotensin (Ang)-aldosterone system as well as blood pressure and re nal hemodynamics. L-Arginine and saline vehicle were iv administered t o 10 healthy male subjects in random order on different days. L-Argini ne infusion (500 mg/kg over 30 min) decreased mean blood pressure (fro m 81.2 +/- 2,7 to 74.0 +/- 2.5 mm Hg; P < 0.001) and renal vascular re sistance (from 0.085 +/- 0.007 to 0.074 +/- 0.306 mm Hg/mL . min; P < 0.01) and increased heart rate (from 60.3 +/- 2.7 to 69.7 +/- 2.1 beat s/min; P < 0.001) and renal plasma flow (fr om 616.6 +/- 37.8 to 701.0 +/- 49,2 mL/min; P < 0.05). L-Arginine reduced serum Ang-converting e nzyme acti;vity (from 10.4 +/- 0.6 to 8.9 +/- 0.5 nmol/mL . min; P < 0 .05) and plasma Ang-II (from 19.3 +/- 3.3 to 12.7 +/- 2.8 pg/mL; P < 0 .001), but had no effect on PRA or the glomerular filtration rate. The saline vehicle did not alter any of these parameters. The iv administ ration of L-arginine (endothelium-derived relaxing factor/nitric oxide ) may reduce the plasma Ang-II concentration by inhibiting Ang-convert ing enzyme. The mechanism by which L-arginine infusion decreases blood pressure can be at least in part explained by inhibition of the renin -Ang system.