Inhibition of nitric oxide activity by arginine analogs in human renal arteries

Plasma levels of endogenous guanidine compounds are increased in various pathologic conditions, including chronic renal failure. In the present study we tested the effects of some of these compounds on basal and stimulated nitric oxide activity in human renal arteries. Rings from human renal arteries were obtained from 22 patients undergoing nephrectomy. The rings were suspended in organ baths for isometric recording of tension. We then studied the effects of NG-monomethyl-l-arginine (L-NMMA), NG,NG-dimethyl-l-arginine (asymmetrical dimethylarginine [ADMA]), aminoguanidine (AG), and methylguanidine (MG) on artery rings under basal and stimulated conditions. In precontracted arteries, L-NMMA (1 μmol/L to 1 mmol/L) and ADMA (1 μmol/L to 3 mmol/L) caused concentration- and endothelium-dependent contractions (median effective concentrations [EC50] = 13.3 μmol/L and 17.5 μmol/L, respectively; Emax = 15 ± 4% and 17 ± 4% of the response to 100 mmol/L KCl, respectively). Aminoguanidine (0.01 to 3 mmol/L) and MG (0.01 to 3 mmol/L) produced endothelium-independent contractions (Emax = 9 ± 3% and 16 ± 2% of the response to 100 mmol/L KCl, respectively). l-arginine (1 mmol/L) but not d-arginine (1 mmol/L) prevented the contractions by L-NMMA and ADMA, but did not change contractions induced by AG and MG. In precontracted arteries, the relaxation to acetylcholine was decreased but not abolished by L-NMMA and ADMA. The remaining relaxation was reduced by charybdotoxin (0.1 μmol/L) and tetraethylammonium (1 mmol/L). The results demonstrate that L-NMMA and ADMA reduce basal and stimulated nitric oxide activity in human renal arteries. An increase in the plasma concentrations of methylarginines associated with renal disease should be considered as a risk factor for endothelial dysfunction and abnormal vasomotor tone in human renal arteries.