Neurotensin-like immunoreactivities in human plasma: feeding responses and metabolism.
Feeding responses and day and night levels of plasma concentration of neurotensin (NT) and NT-fragments were studied in healthy subjects. Plasma levels were measured by three radioimmunoassays recognizing intact NT in addition to C- and N-terminal immunoreactivity. The metabolism of NT was studied following intravenous administration. In 106 subjects fasting levels of intact NT (median 18 pmol/l), C-terminal (median 30 pmol/l) and N-terminal immunoreactivity (median 95 pmol/l) were unrelated to sex or age. Postprandially plasma levels in seven subjects measured with all assays increased by a factor 1-3. Following a mixed meal the increase was biphasic, whereas the response to dairy cream was monophasic. Repetitive measurements during 24 hours showed that levels of N-terminal immunoreactivity fluctuated in a manner related to meal ingestion and were elevated throughout the daytime, whereas intact NT and C-terminal immunoreactivity changed little. Following intravenous infusion of 2.4 pmol/kg/min NT in 5 subjects the chromatographic pattern was similar to that seen postprandially. The plasma half life of intact NT and C-terminal immunoreactivity was 1.5 and 1.2 min, whereas that of N-terminal immunoreactivity was 10.0 min. The differences in circulating levels could be explained by these differences in metabolism, but the physiological significance remains to be elucidated.
D000328:Adult; D002940:Circadian Rhythm; D004435:Eating; D005260:Female; D006207:Half-Life; D006801:Humans; D007106:Immune Sera; D007700:Kinetics; D008297:Male; D009496:Neurotensin / Q000097:blood* / Q000378:metabolism; D011863:Radioimmunoassay / Q000379:methods; D013997:Time Factors
D007106:Immune Sera; D009496:Neurotensin