β-Endorphin is an endogenous 31-amino acid neuropeptide and opioid receptor agonist that binds to μ-, δ-, and κ-opioid receptors (Kis = 3.73, 5.02, and 32.7 nM, respectively, in COS-1 cells expressing rat receptors).1 It binds to rat and mouse brain membrane preparations (IC50s = 0.33 and 0.67 nM, respectively) and induces chemotaxis of human monocytes in vitro when used at a concentration of 0.1 pM.2,3,4 Intracerebroventricular administration of β-endorphin increases the latency to tail withdrawal in response to thermal stimuli in mice with a median antinociceptive dose (AD50) value of 27 pmol per animal.2 It also increases preference for the drug-paired place in a conditioned place preference test when administered to rats intracerebroventricularly at a dose of 5 μg.5
1.Mansour, A., Hoversten, M.T., Taylor, L.P., et al.The cloned μ, δ and κ receptors and their endogenous ligands: Evidence for two opioid peptide recognition coresBrain Res.700(1-2)89-98(1995) 2.Hammonds, R.G., Jr., Nicolas, P., and Li, C.H.β-Endorphin-(1-27) is an antagonist of β-endorphin analgesiaProc. Natl. Acad. Sci. U.S.A.81(5)1389-1390(1984) 3.GarzÓn, J., and SÁnchez-BlÁzquez, P.αN-acetyl derivatives of β-endorphin-(1-31) and -(1-27) regulate the supraspinal antinociceptive activity of different opioids in miceLife Sci.48(14)1417-1427(1991) 4.Sacerdote, P., and Panerai, A.E.Analysis of the beta-endorphin structure-related activity on human monocyte chemotaxis: Importance of the N- and C-terminalPeptides10(3)565-569(1989) 5.Bals-Kubik, R., Herz, A., and Shippenberg, T.S.β-endorphin-(1-27) is a naturally occurring antagonist of the reinforcing effects of opioidsNaunyn Schmiedebergs Arch. Pharmacol.338(4)392-396(1988)