Exogenous L-arginine attenuates the effects of angiotensin II on renal hemodynamics and the pressure natriuresis-diuresis relationship

Abstract

Administration of exogenous L-arginine (L-Arg) attenuates angiotensin-II (AngII)-mediated hypertension and kidney disease in rats. The present study assessed renal hemodynamics and pressure diuresis-natriuresis in anaesthetized rats infused with vehicle, AngII (20 ng/kg per min i.v.) or AngII + L-Arg (300 μg/kg per min i.v.). Experiments in isolated aortic rings were carried out to assess L-Arg effects on the vasculature. Increasing renal perfusion pressure (RPP) from ~100 to 140 mmHg resulted in a nine- to tenfold increase in urine flow and sodium excretion rate in control animals. In comparison, AngII infusion significantly reduced renal blood flow (RBF) and glomerular filtration rate (GFR) by 40-42%, and blunted the pressure-dependent increase in urine flow and sodium excretion rate by 54-58% at elevated RPP. Supplementation of L-Arg reversed the vasoconstrictor effects of AngII and restored pressure-dependent diuresis to levels not significantly different from control rats. Dose-dependent contraction to AngII (10(-10) mol/L to 10(-7) mol/L) was observed with a maximal force equal to 27 ± 3% of the response to 10(-5) mol/L phenylephrine. Contraction to 10(-7) mol/L AngII was blunted by 75 ± 3% with 10(-4) mol/L L-Arg. The influence of L-Arg to blunt AngII-mediated contraction was eliminated by endothelial denudation or incubation with nitric oxide synthase inhibitors. Furthermore, the addition of 10(-3) mol/L cationic or neutral amino acids, which compete with L-Arg for cellular uptake, blocked the effect of L-Arg. Anionic amino acids did not influence the effects of L-Arg on AngII-mediated contraction. These studies show that L-Arg blunts AngII-mediated vascular contraction by an endothelial- and nitric oxide synthase-dependent mechanism involving cellular uptake of L-Arg.

Keywords: L-arginine; blood pressure; nitric oxide; rats.

Figure 1

Effect of saline, Ang II (20 ng/kg/min, iv) or Ang II + L-Arg (300 µg/kg/min, iv) infusion on urine flow (top), urinary sodium excretion (middle), and fractional sodium excretion (lower) in response to increasing renal perfusion pressures (RPP) in volume expanded SD rats. †P<0.05 vs low and med RPP in the same grp, * P<0.05 vs saline and Ang II+ L-Arg at high RPP (n=8–12/group).

Figure 2

Effect of saline, Ang II (20 ng/kg/min, iv) or Ang II + L-Arg (L-Arg: 300 µg/kg/min, iv) infusion on glomerular filtration rate (GFR) (top) and renal blood flow (RBF) (bottom) in response to increasing renal perfusion pressures in volume expanded SD rats. †P<0.05 vs low and med RPP same group, * P<0.05 at respective RPP’s vs saline and Ang II + L-Arg group (n=8–12/group).

Figure 3

Effect of saline vehicle followed by Ang II (20 ng/kg/min, iv) or saline vehicle followed by Ang II+ L-Arg (L-Arg: 300 µg/kg/min, iv) infusion on renal cortical blood flow (top), renal outer medullary blood flow (middle), and renal inner medullary blood flow as measured by laser-Doppler flowmetry in volume-expanded SD rats. *P < 0.05 vs saline infusion (n=10/group).

Figure 4

Urinary nitrate/nitrite excretion (nmol/min) during acute infusion of saline, Ang II (20 ng/kg/min, iv) and Ang II + L-Arg (300 µg/kg/min, iv) in the same group of rats. *P<0.05 vs saline and Ang II infusion (n=4)

Figure 5

Comparison of contractile force generated in endothelium-intact or physically denuded (E-) aortic rings pre-incubated with vehicle or 10⁻⁴M L-Arg in response to incrementing doses of Ang II (10⁻¹⁰M to 3X10⁻⁷M) (top). Comparison of contractile force generated in aortic rings pre-incubated with vehicle, 10⁻⁴M L-Arg, or 10⁻⁴M D-Arg in response to incrementing doses of Ang II (10⁻¹⁰M to 3X10⁻⁷M) (middle). Comparison of contractile force generated in aortic rings pre-incubated with vehicle, 10⁻⁴M L-Arg, or 10⁻⁴M L-Arg + 10−4M L-NAME in response to incrementing doses of Ang II (10⁻¹⁰M to 3X10⁻⁷M) (bottom). Experiments were performed in parallel on separate aortic ring segments obtained from the same animal. * P<0.05 between groups (n=6–8/group).

Figure 6

Comparison of contractile force generated in aortic rings pre-incubated with vehicle, 10⁻⁴M L-Arg, or 10⁻⁴M L-Arg + excess cationic amino acids (10⁻³M L-Lys, L-Orn, or L-HArg) in response to incrementing doses of Ang II (10⁻¹⁰M to 3X10⁻⁷M) (top). Comparison of contractile force generated in aortic rings pre-incubated with vehicle, 10⁻⁴M L-Arg, or 10⁻⁴M L-Arg + excess neutral amino acids (10⁻³M L-Ser or L-Thr) in response to incrementing doses of Ang II (10−10M to 3X10−7M) (middle). Comparison of contractile force generated in aortic rings pre-incubated with vehicle, 10⁻⁴M L-Arg, or 10⁻⁴M L-Arg + excess anionic amino acids (10⁻³M L-Asp or L-Glu) in response to incrementing doses of Ang II (10⁻¹⁰M to 3X10⁻⁷M) (bottom). Experiments were performed in parallel on separate aortic ring segments obtained from the same animal. * P<0.05 between groups (n=6–8/group).

Figure 7

Changes in DAF fluorescence intensity in rat aortic tissue sections incubated with 10⁻⁶M Ang II, 10⁻⁶M Ang II + 10⁻⁴M L-Arg, or 10⁻⁶M Ang II + 10⁻⁴M L-Arg + 10⁻⁴M L-NAME. *P< 0.05 vs 0 mins within the same group. †P< 0.05 vs Ang II + L-Arg or Ang II + L-Arg + L-NAME at the same time point (n=4/group).