Effect of anaesthesia and surgery on urine flow and electrolyte excretion in different rat strains

The suitability of some commonly used experimental procedures for studying the effect of chronic alterations of sodium excretion on lithium clearance was examined in Wistar rats and Sprague-Dawley rats. The animals were maintained on diets with standardized sodium content for 10 days before the investigation. Urine flow and clearance values were measured in (1) awake unoperated rats, (2) awake catheterized rats and (3) anaesthetized rats of both strains. Awake unoperated and awake catheterized Wistar rats showed almost identical urine flows and clearances of sodium and lithium. Amytal anaesthetized Wistar rats showed significantly depressed urine flows and clearances of sodium, lithium and inulin as compared with awake rats. Awake unoperated and awake catheterized Sprague-Dawley rats showed almost identical clearance values but the urine flow rates were increased about fivefold in the awake catheterized Sprague-Dawley rats. Amytal anaesthetized catheterized Sprague-Dawley rats showed unchanged urine flows and clearance values as compared with awake rats. Inactin anaesthesia reduced the urine flows and clearance values in both Wistar rats and Sprague-Dawley rats. It is concluded that anaesthesia and surgery affect the kidney function to different degrees in different rat strains, amytal anaesthetized Sprague-Dawley rats being the least influenced. If exposure of the kidney is unnecessary, awake catheterized Wistar rats offer a suitable experimental procedure for determination of urine flow and urinary clearances of sodium and lithium.