1. The renal handling of myoglobin has been studied in the isolated perfused rat kidney.
2. Myoglobin was freely filtered. Reabsorption by the renal tubules showed saturation kinetics with a relatively low maximum rate of reabsorption (Tmax) of 27-30 μg min−1 g−1 wet wt. at a perfusate concentration of 70-80 μg/ml. Myoglobin reabsorption is therefore much less than that reported for immunoglobulin light chain or lysozyme in this model.
3. Large increases in sodium and water excretion produced by omission of oncotic agent from the perfusate did not alter the kinetics of myoglobin reabsorption.
4. The use of bovine serum albumin as oncotic agent in the perfusate prevented the tubular reabsorption of myoglobin. Small amounts of albumin are filtered by the isolated perfused kidney and it is postulated that this albumin interferes with tubular reabsorption of myoglobin.