Abstract
Neurotensin-like material was found throughout the gut of the amphibian Necturus maculosus, in both muscle layers and mucosa, and with the highest levels in the intestine. Ion-exchange high-performance liquid chromatography (HPLC) and reversed-phase HPLC revealed several peaks of immunoreactive material, with one closely related to neurotensin 1-6 occurring by both methods. Exogenous neurotensin was excitatory on longitudinal stomach muscle; this excitation was unaffected by tetrodotoxin, indicating a direct effect on the smooth muscle. An inhibitory effect of neurotensin on circular muscle preparations was abolished by tetrodotoxin, revealing an excitatory effect. Noradrenaline and adrenaline were in many cases inhibitory on the circular preparations, an effect that was blocked by the β-adrenergic anztagonist propranolol. Propranolol also blocked the inhibitory effect of neurotensin in approximately 50% of the tests, which suggests an involvement of an adrenergic link in the inhibitory effect of neurotensin on the circular muscle. The results are compatible with the view that a neurotensin-like peptide is involved in a simultaneous phase of shortening and widening of a segment of the stomach.
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