using prototypic ligands for each type of opioid receptors ( mu , delta , kappa , and sigma ) as well as compounds derived from each class of endogenous opioid peptides ( beta-endorphin , enkephalins , and dynorphins ) , we have undertaken the characterization of adrenomedullary opioid binding sites .
C0205753
endogenous opioid
C0013355
dynorphins