The secretion of ileal neurotensin (NT) results from events occurring at the apical and basal side of the N-cells. The hypothesis of a functional relationship between cholinergic and peptidergic neurones with the N-cell was investigated in the present study utilizing the isolated vascularly perfused rat ileum. Intraarterial methacholine (MC, 10(-4) M) evoked a prompt and well sustained release of NT in the portal effluent (plateau value at 500% of basal). This effect was dose-dependent over the range of 10(-6) M to 10(-4) M. Bombesin (B) provoked a dose-dependent peak secretion of NT (800% of basal at 10(-7) M) followed by a rapid return to almost basal levels. The B-induced NT release remained unaltered upon 10(-6) M tetrodotoxin (TTX) or 10(-5) M atropine infusion. Substance P (SP) potently stimulated the release of NT. The maximal response, consisting of a sustained secretion, was observed at a concentration of 10(-7) M (350% of basal) while 10(-6) M SP induced a transient release. TTX or atropine did not reduce significantly the SP-induced secretion of NT. Neurokinin A and B did not increase NT concentrations in the portal effluent. B synergistically increased the secretion of NT induced by SP. Atropine or TTX did not modify the effect of combined SP and B infusion. MC potentiated the release of NT induced by B but not that evoked by SP. Combined infusion of SP, B and MC produced the largest output of NT. In conclusion, B, SP and MC are strong stimulants of NT release in rats. In addition, the cooperative effects of these transmitters argue in favor of a complex functional relationship between the intramural nervous network and the intestinal N-cells in rats.