Gastrointestinal neurotensin receptors: contribution of the aromatic hydroxyl group in position 11 to peptide potency.

Neurotensin structural analogues on tyrosine11 were tested in vitro to determine their ability to contract the fundus or relax the intestine. The rank order of potency was: neurotensin greater than [Phe11]-neurotensin greater than [D-Tyr11]-neurotensin greater than [D-Phe11]-neurotensin. All peptides behaved as full agonists. It is concluded that tyrosine11 is part of the neurotensin pharmacophore; the hydroxyl group increases the affinity not the intrinsic activity of the peptide at the receptor.