Step function input to the rat kidney by shifting between auto- and alloperfusion.

A technique is described that permits instantaneous shifts from autoperfusion of the left kidney of an "experimental" rat to alloperfusion of the same kidney from a "pump" rat (or vice versa). Renal arterial and venous pressures are maintained at normal levels during alloperfusion. The kidney has proved to work satisfactorily during both auto- and alloperfusion as judged from measurements of renal blood flow, urine volume flow, urine osmolality, and fractional extraction of inulin and PAH. The vascular dead space of the system is extremely small. If the blood of the pump rat-experimental rat has been equilibrated with indicator, shifting from auto- to alloperfusion constitutes a practically pure step washin to/washout from the kidney. Reverse effects are obtained by shifting from allo- to autoperfusion. Compared with the bolus injection technique, recirculation problems are minimized because the perfused vascular volume of a single kidney is small compared with the whole-blood volume of the rat.