L-arginine reduces tubular cell injury in acute post-ischaemic renal failure

Background. The pathophysiology of renal ischaemia, resulting in tubular cell injury and leading to acute renal failure (ARF), remains unclear. An ever-increasing number of investigations focus on a possible role of nitric oxide (NO) in regulating circulation during ARF. In this context, we investigated the influence of chronic stimulation or inhibition of NO synthesis, or both, on haemodynamic parameters, histology and plasma renin activity (PRA) after ischaemia-reperfusion injury of rat kidneys. Methods, Experiments were performed on adult, male Wistar rats. Before induction of ARF, a group of animals was treated with a NO synthesis inhibitor (L-NAME) and another group was treated with a precursor of NO synthesis (L-arginine). The animals received those substances for 4 weeks. Control groups received the same amount of tap water for 4 or 8 weeks and were divided into groups with ARF (4 weeks-ARF group and 8 weeks-ARF group) and a sham-operated group. Another group of rats was treated first with L-NAME and then with L-arginine in their drinking water, for 4 weeks for each of these two substances. All parameters were evaluated 24 h after the induction of ischaemic ARF or the sham operation. Results, Our results show that such long-term stimulation of NO release by L-arginine improved renal haemodynamics in the ischaemic form of ARF. Renal blood Bow (RBF) increased by 96% in the L-arginine-treated rats with ARF compared with the group with ARF alone. Inhibition of NO synthesis worsens renal haemodynamics after ARF. However, this aggravation can be reversed by L-arginine. The rate of water reabsorption was reduced in all groups with ARF, but this reduction was least in the group treated with L-arginine. The rate of Na+ reabsorption was reduced in all groups 24 h after renal ischaemia, but a significant decrease was observed after the inhibition of NO synthesis. Histological examination of the kidney specimens showed that morphological changes were least in the rats treated with L-arginine, when compared with all other groups with ARF. Nevertheless, the lesions were most prominent in the L-NAME + ARF group. In this group, the areas of corticomedullar necrosis were more widespread in comparison with other groups, especially the L-arginine group where only swelling of the proximal tubular cells was observed. Treatment with L-NAME was not accompanied by any significant alteration in the plasma concentration of angiotensin I (ANG I), while in the group treated with L-arginine ANG I had a tendency to decrease. Conclusions. Acute post-ischaemic renal failure may be alleviated by administering the NO substrate (L-arginine). NO acts cytoprotectively on tubular epithelial cells in ischaemia-reperfusion injury of rat kidney. Evidence of this comes from both histopathological findings and increased tubular water and sodium reabsorption. However, inhibition of NO synthesis (provoked by L-NAME) worsens renal haemodynamics and aggravates morphological changes after ARF. These aggravations can, however, be reversed by L-arginine

Regional hemodynamics after chronic nitric oxide inhibition in spontaneously hypertensive rats

Background: Inhibition of nitric oxide (NO) synthase by L-arginine analogs is associated with elevation of blood pressure in rats. Because endothelium-dependent vasomotion in different vascular beds is not homogenous, the aim of this study was to characterize and compare regional hemodynamic responses in carotid, femoral, and renal vascular beds after chronic NO inhibition in spontaneously hypertensive rats. The possible role of circulating endothelin and renin angiotensin systems in mediating the effects of chronic NO inhibition was also studied. Methods: Systemic and regional hemodynamics, left ventricular mass, plasma renin activity, and plasma endothelin-l were determined in control and N-omega-nitro-L-arginine methyl ester (L-NAME)-treated (10 mg/kg/day, 4 weeks) spontaneously hypertensive rats. Results: L-NAME treatment increased arterial pressure and total peripheral and regional vascular resistance and decreased cardiac output, stroke volume, and regional blood flow. An in-crease in blood flow ratio and a decrease in vascular resistance ratio between carotid and renal as well as femoral and renal vascular beds in rats treated with L-NAME was found. Blood flow and vascular resistance ratios between femoral and carotid vascular beds remained unchanged. L-NAME increased plasma renin activity and left ventricular weight/body weight ratio, whereas plasma endothelin-l was not modified. Conclusions: The results of this study showed that the renal circulation seemed to be more sensitive to the effects of chronic NO inhibition than carotid and femoral vascular beds. Simultaneous activation of the renin angiotensin system may further potentiate cardiovascular effects of chronic NO inhibition. No evidence that circulating endothelin-l plays a role in this model of hypertension was found. KEY INDEXING TERMS: Nitric oxide; Regional hemodynamics; Plasma renin activity; Endothelin; Spontaneously hypertensive rats