Structure-Activity Relationships of Neuromedin U. I. Contractile Activity of Dog Neuromedin U-Related Peptides on Isolated Chicken Crop Smooth Muscle

Synthetic dog neuromedin U-25(d-NMU-25), U-8(d-NMU-8) and their fragments were examined for contractile activity on chicken crop smooth muscle preparation. The relative activities of d-NMU-25, d-NMU-25 (15-25)-NH2 and d-NMU-8 to porcine neuromedin U-8 (p-NMU-8) were 1.69, 2.54 and 5.78, respectively. High activity of d-NMU-8 may be attributable to the N-terminal pGlu residue, which provides resistance to aminopeptidases. Various NMU-8 analogs, having various amino acids, Nα-acetylated amino acids, D-amino acids, or simple organic acids at position 1, were synthesized and evaluated for contractile activity. None of the substitutions caused a significant decrease of the biological activity. Modification at the N-terminal to give aminopeptidase resistance produced analogs with increased contractile activity, presumably because they were not degraded by soluble enzymes released into the bioassay fluid from isolated chicken crop tissue.