when this method was utilized we found that a series of endogenous opioid peptides and enkephalin analogues , ( d-ala2 , met5 ) -enkephalinamide and ( d-met2 , pro5 ) -enkephalinamide produced dose-related analgesic effects , as determined by the tail pinch test .
C0205753
endogenous opioid peptides
C0014298
enkephalin