Distal nephron function of the rat during lithium chloride infusion.

Distal nephron function of the rat during lithium chloride infusion. Chronic lithium (Li) administration in the rat leads to reduced renal concentration (TCH20) without alterations in renal dilution (CH), To examine the acute effects of lithium on TH2O and C1120, rats were infused with a solution composed of 1% sodium chloride and 1% lithium chloride or a 0.225% lithium chloride solution at rates from 0.06 to 0.5 mI/mm. In six rats, infusion of the sodium-lithium solution resulted in marked inhibition ofT°1120 at any level of osmolar clearance (C02m) when cDmpared to animals receiving 2.2% sodium chloride alone. Administration of amiloride, 40 or 80tg/kg BW/min throughout the experiment, to ten rats infused with the sodium-lithium solution, resulted in marked improvement of T2o to C02m relationship. Infusion of 0.255% lithium chloride to nine rats undergoing water diuresis led to marked reductions in CH2O as a function ofdistal delivery (V) when compared to rats receiving 0.225% sodium chloride alone. Infusion of amiloride did not improve the C1120 to V relationship in ten rats undergoing hypotonic lithium chloride infusion. These studies suggest that lithium interferes with sodium chloride reabsorption in the distal nephron, particularly the loop of Henle, and also reduces the permeability of the collecting duct to water. Amiloride, probably by interfering with lithium transport into collecting duct cells, corrects partially the TH2O defectby preventing water permeability changes. The lack of effect of amiloride in C1120 studies may relate to the fact that collecting duct permeability is already at its lowest. The studies suggest that lithium ions retard chloride reabsorption in the ascending limb as inferred from the C,20 and T1120 studies. Both chloride and sodium ions appear to be required for normal loop function.