Opioid receptor affinity and analgesic activity of O- and C-glycosylated opioid peptides.

O- and C-glycosylation of the mu-agonist dermorphin reduced neither its mu receptor affinity in binding assay nor its agonist potency in guinea-pig ileum assay (GPI). O- and C-glycosylation of the delta-agonist deltorphin reduced its delta-receptor affinity and its agonist potency in mouse vas deferens assay (MVD). O- and C-glycosylated dermorphin, administered i.c.v. and s.c., produced long-lasting antinociception in mice and rats. The ratio between i.c.v. and s.c. antinociceptive ED50 demonstrates facilitated transport into the CNS only for the galactosil peptide. Acetylation significantly reduced penetration of glycopeptides into the CNS indicating that facilitated transport into the CNS exists, but does not depend on the glucose transporter (GLUT-1).