Contribution of renal oxygenases to glycerol-induced acute renal failure in the rat

A study on the effect of cimetidine and L-carnitine on myoglobinuric acute kidney injury in male rats

Myoglobinuric acute renal failure is the most important life threatening complication of rhabdomyolysis. Iron, free radicals, nitric oxide and cytochrome p450 are involved in the pathogenesis of mARF. The aim of this study is to compare the effect of cimetidine, l-carnitine and both agents together on mARF in rats. Forty rats were divided into 5 groups; group I: control rats, group II: myoglobinuric ARF rats, group III: mARF rats received l-carnitine (200mg/kg, i.p.), group IV: mARF rats received cimetidine (150mg/kg i.p.) and group V: mARF rats received both agents together. 48h after glycerol injection, systolic blood pressure was measured. Urine and blood samples were collected to evaluate urine volume, GFR, BUN, creatinine, K, Na, serum creatine kinase, NO and glutathione levels. Kidney specimens were taken to investigate renal cytochrome p450 and for histological examinations. Cimetidine treatment significantly decreased creatinine, BUN, K, Na, SBP and creatine kinase and increased GFR and urine volume compared to group II. l-carnitine exerted similar changes except for the effect on K and GFR. NO was significantly decreased, while renal glutathione and cytochrome p450 were significantly increased in groups treated with l-carnitine or cimetidine as compared to group II. Combined treatment further improved renal functions, creatine kinase, oxidative stress parameters and SBP as compared to each therapy alone. The histological changes confirmed the biochemical findings. Cimetidine and l-carnitine have protective effects - almost equally - against mARF. Using both agents together, minimises the renal injury.

Emerging roles for eicosanoids in renal diseases

PURPOSE OF REVIEW

Eicosanoids are products of arachidonic acid metabolism which have important roles in renal homeostasis and disease. In recent years the development of genetically modified animals and new drugs targeting eicosanoids producing enzymes and receptors has unveiled new roles for eicosanoids in kidney function. This review provides an overview of eicosanoid biosynthesis and receptors and discusses recent findings on their role in acute and chronic renal diseases and in renal transplantation.

RECENT FINDINGS

Products of the cyclooxygenases, 5-lipoxygenase, and cytochrome P450 pathways of arachidonic acid metabolism act through distinct receptors presented at different segment of the nephron. Apart from its role in renal physiology and hemodynamic, eicosanoids actively participate in the pathogenesis of acute and chronic renal diseases and have immunoregulatory role in kidney transplantation.

SUMMARY

The new discoveries on the role of eicosanoids in kidney functions and the development of drugs targeting eicosanoids synthesis or action should help to envisage novel therapeutic approaches for patients suffering from renal diseases.

Eicosanoids and renal vascular function in diseases

Arachidonic acid metabolites are vital for the proper control of renal haemodynamics and, when not properly controlled, can contribute to renal vascular injury and end-stage renal disease. Three major enzymatic pathways, COX (cyclo-oxygenase), CYP450 (cytochrome P450) and LOX (lipoxygenase), are responsible for the metabolism of arachidonic acid metabolites to bioactive eicosanoids. These eicosanoids can dilate or constrict the renal vasculature and maintain vascular resistance in the face of changing vasoactive hormones. Renal vascular generation of eicosanoids is altered in pathophysiological conditions such as hypertension, diabetes, metabolic syndrome and acute renal failure. Experimental evidence supports the concept that altered eicosanoid metabolism contributes to renal haemodynamic alterations and the development and progression of nephropathy. The possible beneficial renal vascular actions of enzymatic inhibitors, eicosanoid analogues and receptor antagonists have been examined in hypertension, diabetes and metabolic syndrome. This review highlights the roles of renal vascular eicosanoids in the pathogenesis of nephropathy and therapeutic targets for renal disease related to hypertension, diabetes, metabolic syndrome and acute renal failure.

Loss of nitric oxide and endothelial-derived hyperpolarizing factor-mediated responses in aging

BACKGROUND

Aging has considerable structural and functional effects on the vascular system of the kidney. One such effect is an alteration in vascular tone which potentially will initiate renal damage. Vascular tone is determined by the balance between vasoconstrictors and vasodilators. Therefore, we hypothesized that aging attenuates vasodilatory responses in the kidney. These changes may be mediated by a loss of nitric oxide and endothelial-derived hyperpolarizing factor (EDHF).

METHODS

The systemic and renal responses of nitric oxide and EDHF were investigated in aging (18 months old) and young (3 months old) Sprague-Dawley rats.

RESULTS

We demonstrated a general loss of vasodilatory responses in the aging kidney. In addition, nitric oxide levels were reduced in the serum and kidney cortex of aging versus young animals, although this was not accompanied with a loss of endothelial nitric oxide synthase (eNOS) protein in the kidney cortex. Aging animals also exhibited a loss in EDHF-mediated vasodilation following stimulation with either acetylcholine or bradykinin in the isolated perfused kidney.

CONCLUSION

These findings indicate that not only a defect in the nitric oxide pathway, but also a loss of EDHF-mediated responses may be responsible for impaired vasodilation in the aging kidney. This may result in enhanced vasoconstrictive responses in aging which potentially will cause renal damage and ultimately a loss in glomerular filtration rate (GFR).