The use of a rat isolated ileal preparation to investigate the release of neurotensin.

An isolated and perfused preparation of rat ileum was used to investigate the effects of cholinergic, adrenergic and bombesin stimuli on neurotensin release into the vascular compartment. A vigorous release of neurotensin like immunoreactivity (NTLI) to 200% above basal values in response to intraluminal infusions of emulsified soybean oil (Intralipid) demonstrated the physiological responsiveness of the preparation. Carbachol significantly stimulated the release of both NTLI and bombesin like immunoreactivity (BLI), with maximal responses at 5 X 10(-9) mol/l carbachol of 100% and 400% above basal values for NTLI and BLI, respectively. Noradrenaline at 10(-6) and 10(-4) mol/l caused no significant release of NTLI but markedly inhibited spontaneous BLI release. Synthetic amphibian bombesin caused a marked release of NTLI to 81% and 100% above basal at infusion concentrations of 5 X 10(-11) and 5 X 10(-10) mol/l respectively. These results suggest that there is either a direct effect of cholinergic agents on the N cells bringing about NTLI release, or an indirect effect via the release of bombesin like peptides from intrinsic gut neurones. This preparation provides a useful model to study the complex neural, paracrine and endocrine interactions in the gastrointestinal tract.