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

Abstract

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.

The Effects ofSyzygium aromaticum-Derived Oleanolic Acid on Kidney Function of Male Sprague–Dawley Rats and on Kidney and Liver Cell Lines

“…The technique is based on the assumptions that Li þ is reabsorbed in the proximal tubules to the same degree as Na þ . 29 Thus, a change in FE Li estimates Na þ amount leaving the proximal tubule if GFR is unchanged. However, this is a controversial technique as there is evidence that lithium can be reabsorbed by the distal nephron under certain conditions such as Na þ and K þ depletion.…”

Mechanisms of proximal tubule sodium transport regulation that link extracellular fluid volume and blood pressure

“…Leyssac and Christensen (25) had shown that Li ϩ (in low concentrations) was handled like Na ϩ in the PT, but not further down the nephron; thus, a change in C Liϩ is a good estimate of the change in volume flow leaving the PT, secondary to inhibition of proximal transport if glomerular filtration rate (GFR) is unchanged.…”

The Validity of Lithium Clearance as an Index of Sodium and Water Delivery from the Proximal Tubules

“…However, the situation in animals on a normal sodium intake is not so clear. Clearance studies in which amiloride has been administered have shown no increase of FEy in anaesthetized rats [6,[22][23][24][25] whereas an increase of FEu of about 3-5% of the filtered load has sometimes been observed in conscious rats [21,[26][27][28], Since, in the latter studies. Cl, did not change whereas GFR fell, the interpretation of the increase of FELi is diffi cult.…”