Kanazawa M, Yasujima M, Kohzuki M, Abe K
Second Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
Nihon Jinzo Gakkai Shi. 1994 Jul;36(7):791-9.
Atrial natriuretic peptide (ANP) is degraded by neutral metalloendopeptidase (EC 3.4.24.11) (NEP), and the kidney is the major site of ANP clearance. The regional distribution of NEP in rat kidney was investigated by an enzymatic method and by in vitro autoradiography. The activity of NEP, measured with an enzymatic fluorimetric method employing N-dansy 1-D-alanyl-glycy 1-L-4-nitrophenylalany 1-glycine as a synthetic substrate, was 18 times higher in the outer stripe and 8 times higher in the inner cortex than in the outer cortex. Low concentrations of NEP were found in the outer cortex, in the inner stripe and in the inner medulla. NEP activity in rat kidney was inhibited by specific NEP inhibitors (phosphoramidon, thiorphan, SCH39370, SCH47896 and SCH48446) at micromolar concentrations. SCH47896 is a phenolic derivative of SCH39370 which can be radioiodinated with 125I. SCH48446 is a di-iodo analog of SCH47896. Thus, [125I]SCH47896 retains the full enzymatic inhibitory activity and full biological potency to bind to the active site of NEP. Autoradiographs using [125I]SCH47896 demonstrated maximal bind to regions of the outer stripe of the outer medulla and to the inner cortex, which was consistent with binding to the deep proximal tubules. These bindings were displaced in a dose-dependent manner by NEP inhibitors. Enalaprilat did not displace [125I]SCH47896 binding. EDTA inhibited these bindings by 90%. The present result suggests that degradation of ANP by NEP occurs mainly in the deep proximal tubules, and that the proximal convoluted tubule in the outer cortex is not a major site of location of NEP.(ABSTRACT TRUNCATED AT 250 WORDS)
心房利钠肽（ANP）由中性金属内肽酶（EC 3.4.24.11）（NEP）降解，而肾脏是ANP清除的主要部位。采用酶法和体外放射自显影术研究了NEP在大鼠肾脏中的区域分布。用N-丹磺酰基-L-丙氨酰甘氨酰-L-4-硝基苯丙氨酰甘氨酸作为合成底物的酶荧光法测定NEP活性，结果显示外髓质外层的活性比外皮质高18倍，内皮质的活性比外皮质高8倍。在外皮质、内髓质外层和内髓质中发现NEP浓度较低。大鼠肾脏中的NEP活性在微摩尔浓度下可被特异性NEP抑制剂（磷酰胺、噻吗洛尔、SCH39370、SCH47896和SCH48446）抑制。SCH47896是SCH39370的酚类衍生物，可被125I放射性碘化。SCH48446是SCH47896的二碘类似物。因此，[125I]SCH47896保留了与NEP活性位点结合的全部酶抑制活性和全部生物学效能。使用[125I]SCH47896的放射自显影片显示，在外髓质外层和内皮质区域有最大结合，这与与深部近端小管的结合一致。这些结合可被NEP抑制剂以剂量依赖性方式取代。依那普利拉不能取代[125I]SCH47896的结合。EDTA可使这些结合减少90%。目前的结果表明，NEP对ANP的降解主要发生在深部近端小管，而外皮质中的近曲小管不是NEP的主要定位部位。（摘要截短于250字）
