Functional and structural rat kidney changes caused by peroral or parenteral lithium treatment

Renal functional and structural changes were studied in rats treated with lithium for 5 months. The lithium was administered in two different ways: in the food or as a daily intraperitoneal injection. In the perorally treated rats serum lithium was relatively constant during the day. In the injected rats serum lithium reached a high peak value just after the injection followed by a decrease to very low values. In all rats an increased water consumption and a reduced renal concentration ability were seen during lithium treatment. Light microscopy showed focal degenerative changes in the distal convoluted tubule and collecting ducts. These changes comprised nuclear and cellular polymorphism and tubular dilatation. The functional as well as the structural changes were most pronounced in the rats treated with peroral lithium, and a correlation between the functional and morphological changes was present. It is concluded that lithium is more harmful to the kidney when the administrations give a relatively constant serum lithium level, such as in peroral administration, than when administration causes great variations, including peak values and very low minimum levels in serum lithium. The reason for this might be that a number of regenerative processes occur only in periods with low lithium concentrations.