We have previously reported that neurotensin (NT) is released from the small intestine and elevated in the hepatic-portal circulation in response to the perfusion of the small intestine with a micellar solution of oleic acid. In order to determine the minimum acyl chain length and whether the presence of a carboxylic acid is necessary for the stimulation of NT release, the small intestine of anesthetized rats was perfused with test solutions of fatty acids of 2-, 4-, 8-, or 18-carbons or fatty alcohols of 2-, 4-, or 8-carbons at a concentration of 1 mM prepared in 2.4 mM taurodeoxycholate in 0.9% NaCl. Blood samples, collected from the superior mesenteric vein immediately before the start of the test perfusion and at 15-min intervals thereafter, were extracted immediately and radioimmunoassayed for NT-like immunoreactivity (NTLI) with a C-terminal-directed antiserum. Perfusions of fatty acids with 4 or more carbons and alcohols of 2 or more carbons resulted in a significant elevation (P less than 0.05) in plasma levels of NTLI above the values obtained before the onset of perfusion. Perfusions with ethanol resulted in a value of 4.3 +/- 0.03 mg/dl (SEM) in blood from the superior mesenteric vein while there was no increase in ethanol levels in the peripheral circulation. Perfusion with taurodeoxycholate and 0.9% NaCl alone had no significant effect on plasma levels of the NTLI. In order to characterize the chemical nature of the elevated NTLI, plasma samples from animals perfused with test solution were collected, extracted, pooled, and subjected to HPLC. NT and its N-terminal metabolite, NT(1-8), were quantitated. NT was defined as material having the same retention time as synthetic NT standard and having comparable measurements using N- and C-terminal-directed antisera. Perfusions of fatty acids of four or more carbons and alcohols of two or more carbons resulted in a 2- to 4-fold increase of both NT and NT(1-8) levels in plasma. It is particularly interesting that perfusion with ethanol (2-carbons) causes an elevation in plasma NT, because perfusion with acetic acid (2-carbons) does not increase NTLI. The fact that perfusion of ethanol is effective in releasing intestinal NT suggests that NT may mediate some of the biological effects observed after the consumption of alcohol.