Postprandial release of neurotensin-like immunoreactivity and its mechanism.

The effects of various ingested materials on plasma neurotensin-like immunoreactivity (NTLI) in humans were investigated using a newly developed, specific radioimmunoassay. Plasma NTLI was determined after its extraction with acid/acetone (recovery 77 +/- 4%). The intraassay and interassay coefficients of variation were 3.6% and 8.9%, respectively. The plasma concentration of human NTLI in normal subjects was 5.6 +/- 2.9 pmol/l and showed no significant sex difference. Ingestion of a test meal (150 g of Campbell's condensed meat soup) caused a biphasic rise in plasma NTLI from a basal level of 5.7 +/- 1.0 pmol/l to 10.8 +/- 1.2 pmol/l after 30 min and 9.6 +/- 1.1 pmol/l after 120 min. Ingestion of 5.5 g fat resulted in a biphasic rise in plasma NTLI from a basal level of 4.8 +/- 0.3 pmol/l to 8.9 +/- 0.3 pmol/l after 15 min and 11.9 +/- 0.4 pmol/l after 90 min. When 100-150 mg of ileal mucosa was perfused with a solution of 2 mEq/l fatty acids, 1 mM or 5 mM sodium taurocholate or 154 mM sodium bicarbonate (NaHCO3), the release of NTLI from the mucosa into the perfusate was 2.3-fold, 4.3-fold and 7.5-fold, respectively, over the base level. These results indicate that NTLI release is stimulated by ingestions of meat soup and fat and that NTLI present in the human ileum is released by the direct actions of solutions of fatty acid, sodium taurocholate, and NaHCO3 on the ileal mucosa. These findings strongly suggest that neurotensin (NT) has a physiological role in gut physiology.