Elsevier

Peptides

Volume 7, Issue 3, May–June 1986, Pages 383-387
Peptides

Article
In vitro degradation of neurotensin in human plasma

https://doi.org/10.1016/0196-9781(86)90002-1Get rights and content

Abstract

To study the degradation of neurotensin in plasma in vitro, fresh human plasma was incubated with neurotensin in the presence and absence of the peptidase inhibitors pepstatin A, EDTA, PMSF and aprotinin. The half-time of disappearance of neurotensin at 37°C was calculated to be 226 min in vitro as opposed to 1.4 min in vivo when measured by radioimmunoassay with a C-terminally directed neurotensin antiserum. Both gel filtration and reversed phase high-pressure liquid chromatography (HPLC) showed that the main degradation product of neurotensin in human plasma in vitro was chromatographically and immunologically identical to neurotensin 1–8 and HPLC also demonstrated the formation of neurotensin 1–11. The loss of neurotensin incubated in human plasma in vitro was greatly reduced by EDTA but not by the other peptidase inhibitors tested. In this respect peptidase(s) responsible for the degradation of neurotensin in plasma differ from those present in brain homogenates. EDTA may be of importance in the preservation of neurotensin in plasma samples.

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    The diffusion of NT to the surrounding structures is not probable, because NT is degraded by peptidases. The half life time of NT at 37 °C was measured 1.4 min in human plasma [51]. Electrophysiological studies proved that NT can modify the firing rate of dopaminergic neurons in the VTA and in the substantia nigra for more than 7 min [52].

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    NT is a 13-amino-acid peptide originally isolated in 1973 from bovine hypothalamus (Carraway and Leeman, 1973). NT could be degraded identically to neurotensin 1–8 and neurotensin 1–11 by human plasma in vitro (Lee et al., 1986). Both central and peripheral actions of NT depend on the recognition of the peptide by specific receptors at the plasma membrane of target cells.

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