The Renal Handling of Lithium: Relation Between Lithium Clearance,Sodium Clearance and Urine Flow in Rats with Diabetes Insipidus

Abstract: In order to study the renal handling of lithium, I examined the relation between the lithium clearance and the urine flow in rats which had hereditary lack of vasopressin production and which had been given a test dose of lithium. The two variables were altered by varying the sodium intake. Rats with a low, medium and high sodium intake had a mean lithium clearance of 0.04, 0.22, and 0.40 ml/min./100 g body weight, respectively. When the sodium intake was increased from a medium to a high level, the lithium clearance and the urine flow rose in proportion to each other (r = 0.90). When the sodium intake was decreased from a medium to a low level, the lithium clearance fell relatively more than the urine flow so that the proportion between the two was changed. The experiments show that when vasopressin-induced alterations of the urine flow are excluded and when the sodium intake is not extremely low, proportionality may occur between the lithium clearance and the urine flow. This suggests that the lithium clearance varies in proportion to and is determined by the delivery of sodium from the proximal tubules.