Evidence that (Glu4)-neurotensin is the naturally occurring neurotensin in plasma.

Neurotensin (NT) is a tridecapeptide (less than Glu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu-OH). It has been suggested that the naturally occurring neurotensin in (Gln4)-NT and that it can be hydrolysed to (Glu4)-NT during extraction. The aim of the present study was to determine whether the neurotensin found in human and rat plasma after fat ingestion is (Gln4)-NT or (Glu4)-NT. Two neurotensin antisera are described that have high avidity for (Glu4)-NT but low avidity for (Gln4)-NT. (Gln4)-NT could be separated from (Glu4)-NT by ion-exchange chromatography. The plasma samples were analyzed without prior extraction to avoid hydrolysis of the naturally occurring peptide. The results indicate that neurotensin in unextracted human and rat plasma is present as (Glu4)-NT, as originally proposed by Carraway and Leeman [4].