Localization of neutral endopeptidase in the kidney determined by the stop-flow method

Recently, the existence of neutral endopeptidase (NEP) as a new kininase in the kidney has been reported. In this study, the localization of NEP in the nephron was investigated and compared with other components of the renal kallikrein-kinin (K-K) system by using a stop-flow method in dog kidneys. The stop-flow method was performed according to the procedures previously reported by Scicli et al and Malvin et al. Five mongrel dogs (weighing 15-20 kg) were used in this study. Kininase I, II and NEP were measured by the modified procedure of Ura et al. Kallikrein and kinin were found in the distal tubules, and kininase I and II were observed in both the distal and proximal tubules. NEP was localized mainly in the proximal tubules. A small peak was also recognized in the distal tubules. From these results, it was suggested that, not only kininase I and II but also NEP existing in the proximal tubules may destroy kinin filtered from the glomeruli, and these kininases existing in the distal tubules may play an important role in connection with kinin producing enzymes on the regulation of activity in the renal kallikrein-kinin system.