nitroarginine and Uremia

Topics: Anemia; Animals; Arginine; Bleeding Time; Blood Platelets; Endothelium, Vascular; Enzyme Inhibitors; Erythropoietin; Guanidines; Hemorrhage; History, 18th Century; History, 20th Century; Humans; Isoenzymes; Kidney Failure, Chronic; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; omega-N-Methylarginine; Rats; Succinates; Uremia

In rats undergoing renal mass reduction (RMR) oral supplementation with the nitric oxide (NO) precursor L-arginine increases glomerular filtration rate and ameliorates signs of glomerular injury, suggesting that chronic renal failure in the rats is a condition of low NO formation in the kidney. On the contrary, data are available that in the systemic circulation of uremics, both rats and human beings, NO is formed in excessive amounts and may contribute to platelet dysfunction and bleeding tendency, well-known complications of uremia. The present study was designed to clarify the pathophysiology of renal and systemic NO synthesis in uremia. We showed that renal ex vivo NO generation, measured as the conversion of [3H] L-arginine to [3H] L-citrulline, was lower than normal in RMR rats, seven days after surgery, and progressively worsened with time in close correlation with signs of renal injury. Consistent with these results, urinary excretion of the stable NO metabolites, NO2-/NO3-, significantly decreased in rats with RMR. To go deeper into the cellular origin and biochemical nature of this abnormality we used two histochemical approaches that could locate either NO synthase (NOS) catalytic activity (NADPH-diaphorase) or NOS isoenzyme expression (immunoperoxidase). NADPH-diaphorase documented a progressive loss of renal NOS activity in RMR rats that co-localized with a strong progressive decrease of inducible NOS isoenzyme (iNOS) immunostaining. At variance with iNOS, endothelial cell NOS (ecNOS) staining was rather comparable in RMR and control kidneys. At variance to the kidney, in the systemic circulation of RMR rats the synthesis of NO increased as reflected by higher than normal plasma NO2-/NO3- concentrations. High systemic NO likely derives from vessels as documented by the increased NOS activity and higher expression of both iNOS and ecNOS in the aorta of RMR rats. Up-regulation of systemic NO synthesis might be an early defense mechanism against hypertension of uremia. On the other hand, more NO available to circulating cells may sustain the bleeding tendency, a well-known complication of uremia.

Topics: Animals; Enzyme Inhibitors; Immunohistochemistry; In Vitro Techniques; Kidney; Male; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Rats; Rats, Sprague-Dawley; Time Factors; Uremia

1. Transport of L-arginine and the nitric oxide synthase inhibitors NG-monomethyl-L-arginine and NG-nitro-L-arginine was investigated in human erythrocytes from healthy donors and uraemic patients on haemodialysis. 2. Although K(m) values for total L-arginine influx were not significantly different in erythrocytes freshly isolated from controls or uraemic patients, uraemia was associated with an increase in the Vmax for transport (826 compared with 1176 mumol h-1 l-1 of cells) which was reduced to control values after dialysis. 3. Saturable influx of L-arginine was mediated by the classical cationic amino acid transport system y+ and system y+L, known to transport cationic and neutral amino acids with higher affinity. 4. Under zero-trans conditions, the Vmax for L-arginine transport via system y+increased from 271 to 700 mumol h-1 l-1 of cells in uraemia, while K(m) values increased from 44 to 94 mumol/l. Dialysis had no significant effect on the kinetic parameters altered by uraemia. 5. Under zero-trans conditions, and with system y+ inhibited by N-ethylmaleimide (0.2 mmol/l), transport of L-arginine via system y+L was unaffected by uraemia. 6. Saturable influx of NG-monomethyl-L-arginine was also mediated by systems y+ (K(m) = 56 mumol/l, Vmax = 353 mumol h-1 l-1 of cells) and y+L (K(m) = 17 mumol/l, Vmax = 51.3 mumol h-1 l-1 of cells) and, as with L-arginine, uraemia increased the transport capacity for NG-monomethyl-L-arginine. 7. Influx of the neutral nitric oxide synthase inhibitor NG-nitro-L-arginine was not readily saturable. 8. Intracellular concentrations of L-arginine and NG-monomethyl-L-arginine were significantly increased in erythrocytes from uraemic patients when compared with controls, consistent with an increased transport capacity for L-arginine and NG-monomethyl-L-arginine. 9. The present study provides evidence that system y+ mediates the increased transport of L-arginine and NG-monomethyl-L-arginine in human erythrocytes from patients with chronic renal failure. Our findings may have implications for the activity of the L-arginine-nitric oxide signalling pathway in vascular endothelial and smooth-muscle cells in uraemia.

Topics: Adult; Arginine; Biological Transport; Chromatography, High Pressure Liquid; Erythrocyte Membrane; Erythrocytes; Female; Humans; Kidney Failure, Chronic; Male; Middle Aged; Nitric Oxide Synthase; Nitroarginine; omega-N-Methylarginine; Renal Dialysis; Uremia

We investigated whether the recently described endothelium-derived nitric oxide-mediated gastric hyperemia in the uremic rat protects the gastric mucosa against ethanol injury. Uremia was induced by subtotal nephrectomy. Basal gastric mucosal blood flow, measured by a hydrogen gas clearance technique, was significantly higher in uremic than control rats. Continuous intragastric perfusion with 40% ethanol produced significantly less gross and histological lesions in uremic than in control rats. The administration of 3 mg/kg of NW-nitro-L-arginine methyl ester, a specific inhibitor of nitric oxide biosynthesis, decreased resting gastric mucosal blood flow to control levels in uremic rats, but had no effect on basal gastric blood flow in control rats. This pretreatment with the inhibitor of nitric oxide biosynthesis increased 40% ethanol-induced gastric mucosal lesions in uremic rats to the same level as that observed in control rats, but had no effect on lesions in control rats. In conclusion, this study suggests that in the uremic rat, gastric hyperemia, mediated by increased endothelium-derived nitric oxide, attenuates ethanol-induced gastric mucosal injury.

Topics: Animals; Arginine; Ethanol; Gastric Mucosa; Male; Nitric Oxide; Nitroarginine; Rats; Rats, Inbred Strains; Regional Blood Flow; Uremia