Beneficial and harmful effects of L-arginine on renal ischaemia.
BACKGROUND
The role of nitric oxide (NO) in acute renal failure (ARF) is not yet completely understood. L-Arginine (L-arg) is protective against different ARF models, while L-arg addition in isolated proximal tubules enhances hypoxia/reoxygenation (H/R) injury. The aim of this study was to evaluate the effects of L-arg on renal ischaemia.


METHODS
In in vivo studies, Wistar rats were subjected to 60 min renal artery clamping, and renal function was evaluated 2 and 15 days after ischaemia. Four groups were studied: (1) control; (2) acute L-arg (50 mg/kg/bw i.v.); (3) L-nitro-arginine-methyl esther (L-NAME; 0.5 mg/kg/bw i.v.); and (4) chronic L-arg (L-arg 0.25% in drinking water/7 days). For the in vitro studies, proximal tubules (PTs), isolated by collagenase digestion and Percoll gradient, were studied from three groups: (1) untreated; (2) L-arg-treated (L-arg 0.25% in drinking water/7 days); and (3) L-NAME-treated rats (3 mg/kg in drinking water/7 days). PTs were kept oxygenated or subjected to 15 min hypoxia (H-15) and 35 min reoxygenation (R-35). In some experiments, additional doses of L-arg and L-NAME were administered. Cell injury was assessed by lactate dehydrogenase (LDH) release. NO production was evaluated by NO2-/NO3- measurement (Griess reaction) in both urine and isolation medium.


RESULTS
After 2 days, L-arg infusion protected against ischaemia compared with control rats (0.4 vs 0.2 ml/min/100 g, P < 0.001), while neither L-NAME nor chronic L-arg supplementation ameliorated renal function. After 15 days, both acute and chronic L-arg groups showed a higher glomerular filtration rate (0.6 and 0.75 ml/min/100 g) compared with control rats (0.3 ml/min/100 g, P < 0.05) and L-NAME-treated rats (0.2 ml/min/100 g, P < 0.05). Despite similar recovery in both L-arg groups, the mortality rate was 25% in the chronic L-arg group. Tubular function was also better preserved in the acute L-arg group. PTs isolated from L-arg-treated rats were more sensitive to isolation injury. L-Arg addition enhanced H/R injury (44.9 vs 51.8%, P < 0.05), whereas L-NAME addition protected (44.9 vs 24%, P < 0.001) in untreated rats. In L-arg-treated rats, addition of L-arg did not enhance H/R injury (49.6 vs 53.5%, NS) and L-NAME was still protective (49.6 vs 32.3%, P < 0.001). In PTs from L-NAME-treated rats, L-arg addition also did not enhance H/R injury (50 vs 54%, NS) whereas L-NAME was protective (50 vs 27%, P < 0.001). NO2-/NO3- production paralleled L-arg and L-NAME supplementation.


CONCLUSIONS
It was demonstrated that acute L-arg infusion was beneficial in in vivo renal ischaemia while it was harmful in isolated H/R tubules. In contrast, chronic L-arg supplementation was deleterious both in in vivo and in vitro renal ischaemia, suggesting that injurious effects had overcome the beneficial effects during excess NO exposure.
Tomé
L A
LA
Department of Nephrology, University of São Paulo School of Medicine, Brazil.
Yu
L
L
de Castro
I
I
Campos
S B
SB
Seguro
A C
AC
D058186:Acute Kidney Injury / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control; D000818:Animals; D001120:Arginine / Q000008:administration & dosage / Q000494:pharmacology* / Q000633:toxicity*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007511:Ischemia / Q000188:drug therapy* / Q000503:physiopathology; D007668:Kidney / Q000098:blood supply* / Q000187:drug effects* / Q000293:injuries; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000502:physiology; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D015427:Reperfusion Injury / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control
D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester