for the purpose of comparing the structural requirements of opioid receptor subsites interacting with phenylalanine residues of opioid peptides , analogs containing p-nitrophenylalanine ( phe ( pno2 ) ) were synthesized and tested in the guinea pig ileum ( gpi ) and mouse vas deferens ( mvd ) assay as well as in mu- and delta-receptor selective binding assays .
C0034801
opioid receptor
C0140057
delta-receptor