Gastrointestinal neurotensin receptors: lack of modulation by thyrotropin releasing hormone.

To examine whether thyrotropin releasing hormone (TRH) antagonized gastrointestinal neurotensin receptors in isolated segments of the rat fundus, duodenum and ileum, tissues were superfused, mounted and the isometric tension recorded. Picomoles of neurotensin caused concentration-dependent contractions of the fundus and relaxation of the smooth muscles of the small intestine. Preincubation with 1-10 microM TRH failed to antagonize the activity of neurotensin but potentiated neurotensin-induced relaxation of the ileum. Pretreatment of the tissues with 0.6 microM of neuropeptide fragment 1-11, also failed to block the neurotensin-induced effects but produced a significant potentiation of the relaxant action of neurotensin.