Exogenous L-arginine does not affect angiotensin II-induced renal vasoconstriction in man

Aims: It has been suggested that provision of the substrate of nitric oxide (NO) synthesis, L-arginine, might influence the effects of renal vasoconstrictors. We have therefore studied the effects of pretreatment or concomitant administration of L-arginine on angiotensin II (ANG II)-increased renovascular resistance. Methods: The study was conducted in a double-blind, randomized, cross-over design. Eight healthy subjects were assigned to placebo or a continuous intravenous coinfusion of ANG II (5.0 ng kg^-1 min^{- 1}, infusion period 75 min) with L-arginine (17 mg kg^-1 min^-1 infusion period 30 min). Nine further subjects received a continuous infusion of ANG II with or without pretreatment of L-arginine. Changes in renal plasma flow (RPF) were estimated by the steady state clearance of PAH. Results: L- arginine alone increased RPF to 110±10% over baseline (P<0.003). The ANG II- induced decrease in RPF was not affected by pretreatment or coinfusion of L- arginine. Conclusions: Our results demonstrate that a counterregulatory response of the renal vasculature to high levels of ANG II does not depend on exogenous L-arginine. In healthy subjects, this lack of functional antagonism at the renal vasculature is therefore not a result of NO substrate availability.