Analgesic activity of double endorphins in vivo.

The effects of double endorphins DALA2, DYNO2, CASO2 on pain threshold in the rats were compared with those of DALA (D-Ala2-Met5-enkephalinamide). Marked differences in the analgesic potency of the investigated peptides were noted. The most potent analgesic effect was exerted by DALA2. DYNO2 was weaker than DALA and DALA2 due to lack of glycine residue in position 3, probably responsible for the receptor affinity and analgesic activity in vivo. The weak analgesic activity of CASO2 in vivo corresponds with the weak opiate agonistic action of this peptide in vitro [see 7]. All investigated peptides induced changes in animal behaviour when injected i.c.v. The results indicated that among peptides in the novel group of double endorphins, DALA2 is of special interest because of a potent and long lasting analgesic action.