DADLE agonist activity

The potency of [d-Ala2]Leu-enkephalin in GPI and MVD assays is differentially altered when L-Leu is replaced by the D-amino acid, [D-Ala2-D-Leus]enkephalin (DADL) is half as effective as the parent in the ileum test but three times more active in the MVD procedure (see data)(57) DADL is now commonly employed as a selective 5-agonist (see p 356) Thus,... 

DADL, and the GPI/MVD ED50 values. Morphiceptin (of high peptidase resistance) was one third as active as morphine in an assay for opioid agonists based on a fall in heart rate in urethane-anesthetized rats after iv administra-tion.(108) The low absolute potency of morphiceptin (about a fifth that of DADL, itself only weakly active at /x-sites), may be due to its lack of Gly3, a residue usually essential for activity in enkephalins (p. 345). 

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