Studies on neurotensin. I. Effects on gallbladder motility.

Effects of neurotensin (NT) on gallbladder contraction were examined both in vivo and in vitro. Cholecystokinin-octapeptide (CCK-8) was used to evaluate the methods used in this study and to compare the action of NT on the gallbladder. In In vivo studies, gallbladder contraction was monitored by strain-gauge force transducers implanted on the surface of the dog gallbladder. Bolus intravenous (IV) injection of NT at doses of 20 and 40 ng/kg caused gallbladder contraction of similar of magnitudes in terms of contractile force, while CCK-8 caused contraction dose-dependently. Continuous IV infusion of NT at doses of 250 and 500 ng/kg/hr, which resulted in an elevation of blood levels of NT comparable with those achieved by endogenous release, induced a transient gallbladder contraction. Both maximum contractile force and onset time of contraction were similar to both does of NT. In contrast, CCK-8 induced gallbladder contraction was sustained during infusion of CCK-8 and was dose-dependent for both maximum contractile force and onset time of contraction. NT-induced gallbladder contraction was completely abolished by atropine treatment. In In vitro studies of longitudinal rabbit gallbladder muscle strips, NT was ineffective, while CCK-8 caused a dose-dependent contraction. The present study shows that NT can stimulate gallbladder contraction in the dog via cholinergic pathways.