Abstract
The goal of present study was to determine the effects of the intravenous (i.v.) administration of neurotensin (NT) on the ovine forestomach and abomasal motility in conscious sheep. NT injection at 0.3 nmol/kg slightly raised abomasal pressure, although the effect was not dose-dependent. A bolus i.v. injection of NT at 1 or 3 nmol/kg significantly inhibited the amplitude of cyclic ruminal contractions. NT injection did not alter omasal motility. Pre-injection of an NT receptor subtype-1 antagonist, SR 48692, at 60 nmol/kg immediately before NT injection did not block the inhibitory effect of NT. In an in vitro study using smooth muscle strips of the rumen dorsal sac, NT application at 0.3–10 μmol/L did not inhibit the bethanechol (BCh, 10 μmol/L)-induced tonic contractions of either the longitudinal and circular muscle strips, nor did NT inhibit the electrical field stimulation (EFS)-induced phasic contractions of the muscle strips. The results suggest that circulating NT selectively inhibits the amplitude of cyclic rumen contractions presumably by inhibiting the gastric center in the medulla oblongata and/or the vagus nerves, but not through its peripheral action. An elevation in the plasma concentration of NT appears able to exert the ileal brake-like effect on ruminal motility in sheep.
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