Bile salts in the distal small intestine are strong stimulants of neurotensin (NT) release, but the underlying mechanisms are not known. They were investigated using an isolated vascularly perfused rat jejuno-ileum preparation. Luminal administration of crude ox bile extract (0.25-1.5%, wt/vol) produced a dose-dependent release of NT-like immunoreactivity (NT-LI), with a maximal effect after infusion of 1% bile extract (500% of basal). Pretreatment of the 1% bile extract with the bile salt-sequestering resin cholestyramine (2%, wt/vol) abolished NT-LI release. Taurocholate (TC), the major bile salt in rats, dose dependently increased the release of NT. The maximal secretion of NT-LI was observed after infusion of 20 mM TC (400% of basal). Taurodeoxycholate (20 mM) was as potent as TC in stimulating NT-LI release, but the threshold concentration of taurodeoxycholate for NT-LI secretion was lower than that of TC. Glycocholate and cholate were 2- to 3-fold less potent than TC in releasing NT-LI over the concentration range 5-20 mM. Luminal infusion of oleic acid (sodium salt; 100 mM) increased by 100% the level of NT-LI in the portal effluent, whereas 20 mM oleate had no effect. In contrast, the micellar form of oleic acid (20 and 100 mM) in bile extract (1%) or TC (20 mM) dose dependently reduced the release of NT-LI induced by bile extract or TC alone. Neither intraarterial tetrodotoxin (10(-6) M), EGTA (2 mM), verapamil (5 x 10(-5) M), nor atropine (10(-5) M) had any effect on TC-induced NT-LI release. These results show that the tauro-conjugated forms of cholic and deoxycholic acid are strong stimulants of NT-LI release. The N-cell response is blunted when bile salts are complexed in the lumen by oleic acid. Finally, bile salt-induced NT-LI release is not mediated by intramural nerves and is not dependent on the activation of calcium channels.