Abstract
The present study was undertaken to investigate the peptidases which degrade peptide hormones, particularly angiotensin II (AII), in the isolated rat nephron segments. These peptidases include leucine aminopeptidase, aminopeptidase A, cystine aminopeptidase, “trypsin-like enzyme(s)”, “chymotrypsin-like enzyme(s)”, postproline cleaving enzyme, and converting enzyme. The metabolic ability of [3H]-AII in each nephron segment, was also studied. The activities of these peptidases were exclusively higher in proximal tubules than in other segments. In the proximal tubule, only “trypsin-like enzyme(s)” showed the highest activity in pars convoluta, however, the other peptidases showed the highest activities in pars recta. The activities of aminopeptidase A, “trypsin-like enzyme(s)”, and post-proline cleaving enzyme, were also high in the glomerulus. The activities of these peptidases were hardly detectable in distal nephron segments. From the investigation of the metabolic ability of [3H]-AII in each nephron segment, AII was found to be highly metabolized both in the glomerulus and in the proximal tubule, especially in the pars recta. AII was converted to angiotensin III (AIII) mainly in the glomerulus. All these findings suggest that peptide hormones including AII filtrated through the glomerulus are metabolized in the proximal tubule and that the conversion from AII to AIII occurs mainly in the glomerulus.
