Intact neurotensin (NT) in human plasma: response to oral feeding.

Neurotensin-like immunoreactivity (NTLI) increases in human plasma postprandially. Intact neurotensin (NT) however, has been found to be a minor component of NTLI, the major components being the N-terminal fragments 1-11 and 1-8. Intact NT is the only known biologically-active form. A radioimmunoassay (RIA) has been developed which employs an antiserum unreactive to 1-11 or smaller N-terminal NT fragments. Using this RIA, intact NT response to a mixed meal has been assessed in 10 healthy humans. Intact NT levels were significantly elevated over basal 15 min after ingestion of the meal and remained so for the duration of the experiment (120 min). The suggestion that intact NT is a circulating hormone has been substantiated. Due to the rapidity of the rise in plasma NT after feeding it is proposed that the initial NT response is mediated by neural or hormonal means, rather than by direct luminal stimulation of the N cell-rich jejunoileum.