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

The Effects of L-Arginine in Hypertensive Patients: A Literature Review

Hypertension (HTN) is a chronic disease that affects more than 972 million people throughout the world, which is usually associated with endothelial dysfunction. Scientists are closely investigating endothelial dysfunction and have recently discovered the endothelium-derived relaxing factor (EDRF) known as NO (nitric oxide), which is derived from a semi-essential amino acid, L-arginine, by the action of endothelial nitric oxide synthase (eNOS). Production of adequate amounts of NO by vascular endothelial cells is essential to maintain normal blood pressure and prevent the development of HTN. Asymmetrical dimethylarginine (ADMA) is an endogenous NOS inhibitor that is increased in those with HTN especially in patients with renal dysfunction. In the present review, the role of L-arginine, arginine transporters, and ADMA in the pathobiology of HTN and their potential clinical significance are discussed.

Endothelin ETA receptor-subtype specific antagonism does not mitigate the acute systemic or renal effects of exogenous angiotensin II in humans

BACKGROUND

Angiotensin II (Ang II) is assumed to play a pathophysiological role in a variety of vascular diseases. Animal studies indicate that these effects are partly attributed to stimulation of endothelin-1 (ET-1) release. The aim of the present study was to investigate whether the acute effects of Ang II on systemic and renal haemodynamics in healthy subjects can be influenced by endothelin ET(A)-receptor blockade.

DESIGN

The study design was balanced, randomized, placebo-controlled, double blind, two-way cross-over, in 10 healthy male subjects.

METHODS

Subjects received stepwise increasing intravenous doses of Ang II (0.65, 1.25, 2.5, 5 ng kg(-1) min(-1) for 15 min per dose level) in the presence or absence of BQ-123 (60 microg min(-1)), a specific ETA-receptor antagonist. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were assessed by the para-aminohippurate and inulin plasma clearance method, respectively. Renal vascular resistance (RVR) was calculated from mean arterial pressure (MAP) and renal plasma flow.

RESULTS

Ang II decreased RPF by 34% and GFR by 9% and increased RVR by 94% and MAP by 27% (ANOVA, P < 0.001 vs. baseline, for all parameters). BQ-123 did not alter these renal and systemic haemodynamic responses to a significant degree. In addition, BQ-123 had no significant haemodynamic effect under baseline conditions.

CONCLUSIONS

Short-term increase of circulating Ang II levels causes systemic and renal pressor effects, which are not mitigated by endothelin ETA-receptor blockade. This suggests that the pressor response to Ang II cannot be accounted for by the acute release of vasoactive ET-1.

Renal hemodynamic effects of L-arginine and sodium nitroprusside in heart transplant recipients

BACKGROUND

Long-term treatment with cyclosporine A (CsA) induces vasoconstriction in the kidney and causes renal impairment. An altered L-arginine (L-Arg)/nitric oxide (NO) pathway may play a key role in CsA nephrotoxicity.

METHODS

We studied the effect of L-Arg (dosage, 17 mg/kg/min over 30 min), the precursor of NO synthesis, and sodium nitroprusside (SNP; dosage, 1.0 microgram/kg/min over 30 min) on renal hemodynamics in a double-blind, placebo-controlled, randomized, three-way cross-over study comprising 12 stable cardiac transplant recipients on long-term CsA treatment, 10 patients with chronic nephropathy not receiving CsA, and 13 healthy controls. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were measured by paraaminohippurate (PAH) and the inulin clearance method, respectively.

RESULTS

In healthy subjects, L-Arg induced an increase in RPF (P = 0.009) and GFR (P = 0.001). By contrast, L-Arg did not induce renal hemodynamic effects in heart transplant patients or patients with chronic nephropathy. SNP reduced RPF (P = 0.050) and GFR (P = 0.005) in patients with chronic nephropathy but did not affect renal hemodynamics in heart transplant recipients or in healthy subjects.

CONCLUSIONS

These data indicate that L-Arg cannot be used to reverse CsA-induced renal vasoconstriction in heart transplant recipients under long-term CsA treatment, although these patients have a normal renal response to SNP.