A NOVEL COMPUTER-DRIVEN, SERVO-CONTROLLED FLUID REPLACEMENT TECHNIQUEAND ITS APPLICATION TO RENAL-FUNCTION STUDIES IN CONSCIOUS RATS

1. A new rat model has been developed allowing body fluid status to be accurately controlled and maintained throughout experimentation by co mputer-driven, servo-controlled replacement of spontaneous urinary flu id losses. 2. Experiments in vitro were performed to test the accuracy of the servo system, and experiments in vivo were carried out to re-a ssess basic renal function in servo-controlled vasopressin-replete Lon g Evans and vasopressin-deficient Brattleboro rats. The model was furt her evaluated in water-diuretic Wistar rats with or without administra tion of a vasopressin V2-receptor agonist, 1-desamino-8-D-arginine vas opressin. 3. The data gained from the present study indicate the suita bility of the servo-controlled replacement system for conscious renal function studies in three different rat strains. Haemodynamic and rena l function variables measured were demonstrated to be stable throughou t a 5 h experimental procedure and reproducible between repeated exper imental occasions over a 14 day post-operative period. 4. Using the se rvo-control technique, the expected action of 1-desamino-8-D-arginine vasopressin on renal water handling was demonstrated, but the natriure tic effect reported by some workers was not evident. 5. Since the serv o-controlled fluid replacement technique maintains many of the inheren t differences between vasopressin-replete Long Evans and vasopressin-d eficient Brattleboro rats and eliminates the changes in body fluid. vo lume during transition from a diuretic to an antidiuretic state, the m odel confers an advantage over previously employed constant infusion p rotocols.