In vivo disposition and metabolism of enkephalins: relationship to analgesic properties.
After intravenous injection, both Met5-enkephalin and D-Ala2-Met5-enkephalinamide rapidly entered the brains of mice. Both peptides obtained similar concentrations. The t-1/2 for D-Ala2-Met5-enkephalinamide in the brain (0.7 minutes) corresponds roughly to its analgesic t-1/2 (1.7 minutes); thus, rapid metabolism appears to account for the short duration of analgesia seen with this compound. Met5-enkephalin, on the other hand, although attaining similar brain concentrations, failed to elicit analgesia. Rapid metabolism alone does not account for this lack of analgesic effect.
D000700:Analgesics; D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects; D004723:Endorphins / Q000378:metabolism*; D004745:Enkephalins / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D010084:Oxidation-Reduction; D011930:Reaction Time / Q000187:drug effects; D013997:Time Factors
D000700:Analgesics; D004723:Endorphins; D004745:Enkephalins