Handling of small peptides by rat renal tubules

Academic Article

Abstract

  • Previous studies from our laboratories have shown that a substantial percentage of 14C angiotensin II is rapidly removed from proximal but not distal tubules of the rat by a combination of enzymatic cleavage and reabsorption of most of the products. To evaluate the specificity and kinetics of reabsorption of small peptides, 3H bradykinin (3H Bk) and 14C inulin were infused into individual rat nephrons and urinary excretion measured. 3H Bk and its urinary metabolites were identified by two dimensional peptide mapping. Recovery of 3H labeled material was 24.1% when proximal tubules were infused and 98.1% when distal tubules were infused. For proximal tubules, 90% of the labeled material recovered from urine appeared as metabolites of Bk; for distal tubules, almost 100% was intact Bk. Timed urine collection showed a 30 second delay in appearance of 3H labeled material in comparison with 14C inulin, demonstrating the rapidity of enzymatic cleavage. When either unlabeled angiotensin I or BK was infused in 800:1 molar excess with 3H Bk into proximal tubules, recovery of labeled material greatly increased and was a function of tubular length. Results indicate that proximal tubular cells have a high capacity mechanism for rapid enzymatic digestion and removal of these small peptides from luminal fluid that is not highly specific.
  • Published In

  • Clinical research  Journal
  • Author List

  • Oparil S; Carone FA; Pullman TN; Nakamura S
  • Volume

  • 23
  • Issue

  • 3