Role of endopeptidase 3.4.24.16 in the catabolism of neurotensin, in vivo, in the vascularly perfused dog ileum

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Abstract
1 The degradation of tritiated and unlabelled neurotensin (NT) following close intra-arterial infusion of the peptides in ileal segments of anaesthetized dogs was examined. 2 Intact NT and its catabolites recovered in the venous effluents were purified by chromatography on Sep-Pak columns followed by reverse-phase h.p.l.c. and identified by their retention times or by radioimmunoassay. 3 The half-life of neurotensin was estimated to be between 2 and 6 min. Four labelled catabolites, corresponding to free tyrosine, neurotensin (1–8), neurotensin (1–10) and neurotensin (1–11), were detected. 4 Neurotensin (1–11) was mainly generated by a phosphoramidon-sensitive cleavage, probably elicited by endopeptidase 24–11. 5 Two endopeptidase 3.4.24.16 inhibitors, phosphodiepryl 03 and the dipeptide Pro-Ile, dose-dependently potentiated the recovery of intact neurotensin. Furthermore, both agents inhibited the formation of neurotensin (1–10), the product that results from the hydrolysis of neurotensin by purified endopeptidase 3.4.24.16. In contrast, the endopeptidase 3.4.24.15 inhibitor Cpp-AAY-pAB neither protected neurotensin from degradation nor modifed the production of neurotensin (1–10). 6 Our study is the first evidence to indicate that endopeptidase 3.4.24.16 contributes to the catabolism of neurotensin, in vivo, in the dog intestine.