L-carnitine improves oxidative stress and suppressed energy metabolism but not renal dysfunction following release of acute unilateral ureteral obstruction in rat.

BACKGROUND AND AIM: We recently showed that L-carnitine reduced oxidative stress and suppressed energy metabolism, while α-tocopherol only prevented redox imbalance, in the obstructed kidney of rats subjected to 24-hr of unilateral ureteral obstruction (UUO). The present study was undertaken to investigate the effects of both compounds on disturbed renal hemodynamics, solutes-excretion, and urine-concentrating ability as well as renal oxidative stress and suppressed metabolism at early hours following release of 24-hr UUO. METHODS: UUO was induced in anaesthetized rats that received L-carnitine, α-tocopherol or their vehicles in four different groups. Each rat was re-anaesthetized, prepared for renal functional measurements, and its ureteral obstruction was released at 24-hr. Then, urines of both kidneys were separately collected during 30-90 min of post-release, with taking blood samples at beginning and end of it. Finally, both kidneys were removed and preserved at -80°C for future measuring their levels of ATP and ADP as well as malondialdehyde (MDA) and ferric reducing/antioxidant power (FRAP). There were also sham and control groups. RESULTS: Post-obstructed kidney (POK) of vehicle-treated groups compared to equivalent kidney of sham group had lower ATP, ATP/ADP, FRAP, creatinine clearance, absolute Na(+)- and K(+)-excretion, and effective free-water reabsorption, but higher MDA and ADP. L-carnitine could improve oxidative stress and suppressed energy metabolism and α-tocopherol normalized redox state, but both compounds did not have any effects on altered functional variables of the POK. CONCLUSION: Oxidative stress and suppressed energy metabolism may not be involved in the development of renal dysfunction during acute ureteral obstruction.

Comparison of the effects of L: -carnitine and alpha-tocopherol on acute ureteral obstruction-induced renal oxidative imbalance and altered energy metabolism in rats.

The suppression of renal energy metabolism during ureteral obstruction is a well-known phenomenon; however, its exact responsible mechanism(s) and association with simultaneously induced renal oxidative stress have not been clarified. This study examined the improving effects of L: -carnitine, a facilitating cofactor for mitochondrial oxidation of fatty-acids as well as a scavenger of free-radicals, and alpha-tocopherol as the most potent antioxidant on renal metabolic defect and oxidative stress induced by acute unilateral ureteral obstruction (UUO). The left ureter was ligated in ether-anaesthetised rats, in which L: -carnitine, alpha-tocopherol or their vehicles were intraperitoneally injected in four different groups. After elapsing 24 h of UUO-induction, both kidneys were removed and stored at -80 degrees C. There were also two sham-operated and control groups. The kidney samples were assessed to measure the levels of ferric reducing/antioxidant power (FRAP) and malondialdehyde (MDA) for evaluating their redox state, as well as, their amounts of adenosine triphosphate (ATP) and adenosine diphosphate (ADP) by using luciferin-luciferase method. As much as 24 h of UUO in vehicle-treated groups caused increases in MDA and ADP, but decreases in FRAP, ATP, and ATP/ADP of the obstructed kidney with respect to those of the sham group. alpha-tocopherol normalised the levels of MDA and FRAP but did not affect the altered amounts of energy metabolic indices in the obstructed kidney, while L: -carnitine could ameliorate all of them. These findings suggest that oxidative stress may not involve in development of acute UUO-induced suppression of renal aerobic metabolism, and probably reduction of energy substrates is a responsible factor.

Cooperative mechanisms of acute antidiuretic response to bendroflumethiazide in rats with lithium-induced nephrogenic diabetes insipidus.

The exact mechanism underlying thiazides-induced paradoxical antidiuresis in diabetes insipidus is still elusive, but it has been hypothesized that it is exerted either via Na+-depletion activating volume-homeostatic reflexes to decrease distal delivery, or direct stimulation of distal water reabsorption. This study examined how these two proposed mechanisms actually cooperate to induce an acute bendroflumethiazide (BFTZ)-antidiuretic effect in nephrogenic diabetes insipidus (NDI). Anaesthetized rats with lithium (Li)-induced NDI were prepared in order to measure their renal functional parameters, and in some of them, bilateral renal denervation (DNX) was induced. After a 30 min control clearance period, we infused either BFTZ into 2 groups, NDI+BFTZ and NDI/DNX+BFTZ, or its vehicle into a NDI+V group, and six 30 min experimental clearance periods were taken. During BFTZ infusion in the NDI+BFTZ group, transiently elevated Na+ excretion was associated with rapidly increased urinary osmolality and decreased free water clearance, but Li clearance and urine flow declined in the later periods. However, in the NDI/DNX+BFTZ group, there was persistently elevated Na+ excretion with unchanged Li clearance and urine flow during the experimental period, while alterations in free water clearance and urinary osmolality resembled those in the NDI+BFTZ group. In conclusion, BFTZ initially exerted two direct effects of natriuresis-diuresis and stimulating free water reabsorption at the distal nephron in NDI, which together elevated Na+ excretion and urinary osmolality but kept the urine volume unchanged in the first hour. Thereafter, the resultant sodium depletion led to the activation of neural reflexes that reduced distal fluid delivery to compensate for BFTZ-induced natriuresis-diuresis which, in cooperation with the direct distal BFTZ-antidiuretic effect, resulted in excretion of urine with a low volume, high osmolality, and normal sodium.

The effect of isoprenaline infusion on renal renin and angiotensinogen gene expression in the anaesthetised rat.

In this study, we investigated the ability of acute infusions of isoprenaline to alter renin and angiotensinogen gene expression in the kidney of rats anaesthetised with chloralose-urethane. Groups of rats received I.V. infusions of either saline or the beta-adrenoceptor agonist isoprenaline at 400 ng x kg(-1) x min(-1) for 4 h. The isoprenaline infusion caused a sustained decrease in mean blood pressure of approximately 20 mmHg (P < 0.01), an increase in heart rate of 50 beats x min(-1) (P < 0.01) and reductions in urine flow and sodium excretion of 80-90 % (both P < 0.01). Renal blood flow and glomerular filtration rate were transiently reduced by 21 % (P < 0.01) and 61 % (P < 0.001), respectively, in the first hour, recovering to baseline levels after 4 h of infusion. At the end of the study, plasma renin activity was raised approximately 6-fold (P < 0.01) while renal renin and angiotensinogen mRNA levels were 1.8- and 1.5-fold higher (both P < 0.05) compared to the control group (saline infusion). The isoprenaline-induced renin secretion could have been mediated via the activation of beta-adrenoceptors resulting in the exocytosis of renin-containing granules, with a smaller contribution being due to reduced renal haemodynamics. The increase in renal renin gene expression in response to isoprenaline was probably due primarily to the intracellular signalling processes acting directly on nuclear mechanisms. Similarly, the increased renal angiotensinogen gene expression most probably reflected a direct action of the isoprenaline. These findings provide evidence that catecholamines are involved in mechanisms that rapidly alter the expression of the genes of the renin-angiotensin system within the kidney.