selectivities of these analogs for a single class of opioid receptor were investigated by examining relative potencies in the mouse vas deferens assay , in which the functional receptor is the delta receptor , versus the guinea pig ileum assay , in which the mu receptor is the functional receptor , and by determining their relative abilities to displace the prototypical delta receptor ligand [ d-ala2 , d-leu5 ] enkephalin and the prototypical mu receptor ligand naloxone from rat brain membrane preparations .
C0034801
opioid receptor
C0066908
mu receptor