Interaction of amiloride and lithium on distal urinary acidification

The interaction of amiloride and LiCl administration on renal HCO3 handling was studied in hydropenic rats. Amiloride administration resulted in a significant increase in Na, Cl, and HCO3 excretion, whereas K excretion decreased significantly. LiCl administration resulted in a significant increase in Na, Cl, K, and HCO3 excretion. LiCl administration to animals receiving amiloride led to a significant increase in HCO3 excretion but failed to cause an increase in Na or K excretion. Addition of amiloride to animals receiving LiCl resulted in a significant increase in Na and HCO3 excretion. The net increase in fractional HCO3 excretion seen in this group was greater than that seen in all other groups. The finding that the net increase in FEHCO3 was greater in animals receiving amiloride after administration of LiCl than in animals receiving LiCl after amiloride administration indicates that amiloride blunted the effect of LiCl on HCO3 excretion. Administration of amiloride to both normal rats and to rats infused with Li during HCO3 administration resulted in a significant decrease in U-B Pco2 which could not be explained by the decrease in urine HCO3 concentration. These data demonstrate that amiloride inhibits distal acidification in vivo. LiCl administration also resulted in a decrease in U-B Pco2 which could be explained by the decrease in urine HCO3 concentration. LiCl administration also resulted in a decrease in TcH2O which could be prevented by prior administration of amiloride. These data indicate that amiloride blunts the effect of LiCl on urinary acidification, an effect similar to that observed on urinary concentration. These data suggest that the effect of Li on urinary acidification is in part dependent on Li entry into the cell.