Abnormal tubular permeability in hypothermic perfused kidneys

Isolated canine kidneys perfused with cryoprecipitated plasma at 15 degrees C exhibit unexpectedly low inulin clearance (CIn) and creatinine clearance (CCr) rates. CIn and CCr, as well as p-aminohoppurate (PAH) clearance, varied linearly with urine flow rate, whether the variations in urine flow were spontaneous or induced, either by elevating perfusion pressure or by adding mannitol to the perfusate. Retrograde intraureteral injection (RII) of an isotonic fluid containing dextran, inulin, and PAH, followed by a period of ureteral occlusion and subsequent serial recollection of the injected fluid, revealed that inulin and PAH, relative to dextran, were lost from distal tubular fluid. Similar experiments in anesthetized dogs indicated no loss of inulin or PAH from tubules of in situ kidneys. Renal venous perfusate, collected from isolated kidneys during the low pressure phase of the RII, contained the following percentages of the quantities injected intraluminally: dextran, 9.22%; inulin, 11.0%; and PAH, 22.0%. These data indicate that a low measured glomerular filtration rate in hypothermic perfused kidneys is partly due to diffusion of inulin or creatinine out of the tubular lumen.