Alterations of lithium clearance in rats by different modes of lithium administration

This study examines the effects of acute versus dietary lithium administration on proximal tubular fluid output (Vprox) and sodium clearance in 6 groups of unrestrained, conscious rats. Vprox was estimated on the basis of the renal lithium clearance. The aim was to find the mode of lithium administration which least influences the proximal and distal reabsorption of sodium. The lithium doses used resulted in serum lithium concentrations between 0.2 and 0.3 mmol/l with no difference between the groups. Acute intravenous lithium administration increased lithium clearance by 40% and sodium clearance by 109%. Administration by gastric tube increased lithium clearance by 22% and sodium clearance by 78% in comparison to dietary administration of lithium. Potassium excretion did not change by acute lithium administration. The data presented indicate that prior to measurements of lithium clearance, lithium should be administered in the diet for 2 days, since acute lithium administration, intravenously or by gastric tube, causes great changes in renal tubular reabsorption.