The renal handling of biologically active peptides.

With the use of the protease inhibitor from bovine organs--Trasylol-- as a model, we studied the pinocytic transport of peptides in the kidney. Rats were injected with the 125I-labeled peptide and killed at different times thereafter. Kidney homogenates were subfractionated by differential and sucrose gradient centrifugation. Radioactivity was measured in the fractions in order to study the time-dependent fixation of the peptide to different cell organelles. With short survival periods, the protease inhibitor is recovered in the brush-border fraction, with longer periods, a shift towards the lysosome fraction takes place. Thus, the renal transport of the protease inhibitor consists of three steps: binding to the brush border, incorporation in micropinocytic vesicles and transport in phagolysosomes.