Prostaglandin synthesis inhibition stimulates lithium reabsorption in Henle's loop in rats

Toward the optimal clinical use of the fraction excretion of solutes in oliguric azotemia

While the fractional excretion of solutes have long been considered excellent research tools to investigate tubular physiology, their clinical use has become common over the last 40 years in the diagnoses of many disorders; however, none have reached the clinical utility of the fractional excretion of sodium in the ability to distinguish pre-renal azotemia from acute tubular necrosis. Nevertheless, there are many drugs and medical conditions that interfere with that utility and recently other solutes, including urea, uric acid and lithium, have been recently investigated to improve the diagnostic ability in clinical situations where the fractional excretion of sodium is known to be unreliable. We review the tubular physiology of these solutes and show how the differences in tubular physiology might be exploited to develop a strategy for their optimal clinical use.

Effect of lithium on cyclosporin induced nephrotoxicity in rats

Psychoactive drugs provide essential intervention in the care of transplant recipients, yet little is known of their interaction with immunosuppressants such as cyclosporin (CSA). Lithium (Li) is an invaluable drug for the treatment of manic disorders in organ transplant patients. As both these drugs are known to produce renal toxicity, the concomitant use of CSA and Li may be potentially harmful. The present study was undertaken to investigate the effect of CSA and Li chloride individually and in combination on renal structure and function of rats. Male Sprague-Dawley rats were divided into the following eight groups of seven animals each: group I, control (vehicle only); group 2, Li (2 mEq/ kg i.p.) alone; group 3, CSA 12.5 mg/kg (subcutaneous); group 4, CSA 25 mg/kg; group 5, CSA 50 mg/kg; group 6, CSA 12.5 mg/kg + Li; group 7, CSA 25 mg/kg + Li; and group 8, CSA 50 mg/kg + Li. The drugs were given once a day for seven days; Li being administered 30 min before CSA. Twenty four hours after the last dose of drugs the animals were sacrificed and blood samples were analyzed for blood urea nitrogen (BUN), serum creatinine (SCr), CSA and Li levels. The left kidney was analyzed for malondialdehyde (MDA) and conjugated dienes (CD) levels and right kidney was used for histopathological studies. Our results showed that Li alone did not produce any significant renal toxicity, whereas CSA dose dependently caused structural and functional changes in kidneys. However, significantly higher structural and functional impairment was observed in the animals treated with Li plus CSA as compared to CSA alone treated animals. Several fold increase in blood Li level was also noticed in the rats concomitantly treated with CSA and Li. A significant increase in MDA and CD in the rats treated with CSA plus Li suggests the role of oxidative stress in drug induced nephrotoxicity. These findings clearly demonstrate that even non toxic doses of Li may significantly exacerbate CSA induced nephrotoxicity in rats. The enhanced nephrotoxicity following concomitant use of these drugs may be attributed to significant increase in the bioavailability of Li and enhanced oxidative stress. Further clinical studies are warranted to investigate the interaction of these nephrotoxic drugs in human subjects.

Renal tubular lithium reabsorption in potassium-depleted rats

1. In order to identify the tubular sites responsible for the reduced fractional excretion of lithium (FELi) during potassium depletion, free-flow micropuncture was performed in anaesthetized rats that had been fed a low potassium (low-K+) diet or a control diet for 5-6 days. FELi in low-K+ rats was 0.09 +/- 0.02, compared with 0.25 +/- 0.01 in control animals. 2. Fractional water reabsorption in proximal convoluted tubules was enhanced in potassium-depleted rats. However, fractional lithium reabsorption was not. Consequently, the tubular fluid-to-plasma lithium concentration ratio at the late proximal convoluted tubule was raised in the low-K+ animals (1.50 +/- 0.03 vs. 1.18 +/- 0.02; P < 0.001). 3. Fractional lithium delivery to the early distal tubule in low-K+ rats (0.31 +/- 0.01) was similar to that in control animals (0.30 +/- 0.02). However, whereas in control rats there was no significant difference between early and late distal tubular deliveries of lithium, late distal fractional lithium delivery in the low-K+ group was reduced markedly (to 0.10 +/- 0.01). 4. Treatment of potassium-depleted rats with amiloride had no effect on lithium reabsorption in the proximal convoluted tubule or loop of Henle. However, fractional lithium delivery to the end of the distal tubule was increased slightly (to 0.15 +/- 0.02; P < 0.05) and FELi was increased substantially (to 0.22 +/- 0.01; P < 0.001). 5. It is concluded that two factors contribute to the reduced FELi seen in potassium-depleted rats: lithium reabsorption in the superficial distal tubules and amiloride-sensitive lithium reabsorption in the collecting ducts. The data also suggest heterogeneity with respect to lithium handling between superficial and deep nephrons during potassium depletion.

A comparison between endogenous and exogenous lithium clearance in the anaesthetized rat

The present study tests whether the endogenous renal lithium clearance (CLi) may be used as an alternative to the conventional method in order to avoid the adverse effects of exogenous lithium on renal function. Endogenous CLi) was measured by flameless atomic absorption spectrometry (AAS) in halothane anaesthetized, laparotomized rats and compared with values obtained after subsequent intravenous (i.v.) administration of LiCl. Endogenous plasma lithium concentration (PLi) was 0.30 +/- 0.06 mumol l-1. When measured by both conventional flame emission AAS and flameless AAS on the same samples, values for PLi did not differ significantly. Endogenous CL1/GFR was 0.195 +/- 0.01 (mean +/- SEM). Amiloride caused on significant change in either the endogenous CLi or 51Cr-EDTA clearance, a measure of glomerular filtration rate (GFR), but it caused a significant increase in CNa. Administration of exogenous Li+ had no significant effect on CLi (230 +/- 33 vs. 234 +/- 35 microliters min-1 gKW-1); both urine flow and CNa increased significantly (P < 0.01) (5.4 +/- 0.4 vs. 9.6 +/- 1.3, and 2.4 +/- 0.5 vs. 10.7 +/- 2.4 microliters min-1 gKW-1, respectively). GFR and calculated proximal tubular reabsorption rate (APR) both decreased by approximately 100 microliters min-1 gKW-1 (both P < or = 0.025), suggesting a moderate inhibition of APR after the acute elevation of plasma Li+ concentration. It is concluded that the endogenous CLi may be used as an alternative to the conventional method.