Biological potency of neurotensin metabolites in vivo: importance of alcohol 'fixation' of blood.
Neurotensin (NT), a 13-amino acid peptide, is released from the ileum following a meal. It is metabolized principally by the kidney and in the circulation to N-terminal fragments and apparently rapidly degraded C-terminal fragments. The present study was designed to compare the biological activity (plasma pancreatic polypeptide response) and the clearance kinetics of NT(1-13), the N-terminal fragment NT(1-11) and the C-terminal fragment NT(8-13). To measure accurately the circulating concentrations of short-lived NT fragments in the circulation, a method was devised of collecting blood directly into alcohol ('alcohol fixation'). The alcohol fixation procedure prevented the post-collection losses of the C-terminal fragment NT(8-13) and established that, based on blood levels achieved, NT(8-13) had 70% of the pancreatic polypeptide stimulating potency of NT(1-13). Nevertheless, the metabolic clearance rate of NT(8-13) was about sevenfold higher than the intact molecule, NT(1-13), suggesting that circulating C-terminal fragments have a minor physiological role. When the N-terminal fragment NT(1-11) was infused, there was no sustained effect on pancreatic polypeptide secretion although it was cleared at a rate similar to that of NT(1-13). It is concluded that the use of alcohol fixation prevents post-collection losses of NT fragments and enables true biological potencies of short-lived fragments to be assessed. The biological activity of NT resides in the C-terminus which, once split from the protective N-terminus, is rapidly degraded in the circulation. The remaining intact but inactive N-terminus is relatively stable.
Shulkes
A
A
Department of Surgery, University of Melbourne, Austin Hospital, Victoria, Australia.
Fletcher
D R
DR
Hardy
K J
KJ
D000818:Animals; D001800:Blood Specimen Collection / Q000379:methods; D000431:Ethanol; D008657:Metabolic Clearance Rate; D009496:Neurotensin / Q000378:metabolism*; D010191:Pancreatic Polypeptide / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D011863:Radioimmunoassay; D012756:Sheep
D010446:Peptide Fragments; D009496:Neurotensin; D000431:Ethanol; D010191:Pancreatic Polypeptide; C054381:neurotensin (8-13); C059582:neurotensin (1-11)