Opioid transportation from blood-brain

As briefly reported the synthesis of an ideal analgesic asks for an improvement of both pharmacodynamic and in pharmacokinetic peculiarities. Sometimes if pharmacodynamic properties are improved, the pharmacokinetic characters can be still far from those of a perfect analgesic molecule. The quantities of opioids normally transported into the CNS can be low, and inadequate blood-brain barrier (BBB) permeation can be responsible for not optimized or for the different analgesic potencies among different opioid analogues. Consistently one major avenue of investigation involves the development of opioid analogues that penetrate the blood-brain-barrier (BBB). 

Various peptides from the enkephalin family, or analogs of these molecules, permeate through the blood-brain barrier at different rates, often by different mechanisms [49]. For example, D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (a cyclic peptide that binds to jU.-opioid receptors, in which Pen is penicillamine) permeates by diffusion only Tyr-D-Pen-Gly-Phe-D-Pen ([d-Penj -enkephalin, a cyclic Met-enkephalin analog that binds to 5-opioid receptors) permeates by diffusion and a saturable transport mechanism (Tyr-D-Ala-Gly-Phe-NH)2 (biphalin, a dimeric analog that is active at fx-... 

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