Glycyl-L-glutamine is a C-terminal dipeptide fragment of β-endorphin .1 It decreases reperfusion damage and increases the time to ischemic contracture in isolated rat hearts in a model of cardiac ischemia-reperfusion injury using eight- and 36-week old rats when used at a concentration of 5 mM.2 Glycyl-L-glutamine (1-100 nmol) inhibits morphine-induced respiratory depression with no effect on morphine-induced analgesia in rats.3 It also inhibits acquisition of place preference, delays the development of tolerance, and reduces withdrawal intensity in morphine-conditioned rats.4
1.Parish, D.C., Smyth, D.G., Normanton, J.R., et al.Glycyl glutamine, an inhibitory neuropeptide derived from β-endorphinNature306(5940)267-270(1983) 2.Almashhadany, A., Alghamdi, O.A., Van der Touw, T., et al.?-Glycyl-?-glutamine provides the isolated and perfused young and middle-aged rat heart protection against ischaemia-reperfusion injuryAmino Acids47(8)1559-1565(2015) 3.Owen, M.D., Unal, C.B., Callahan, M.F., et al.Glycyl-glutamine inhibits the respiratory depression, but not the antinociception, produced by morphineAm. J. Physiol. Regul. Integr. Comp. Physiol.279(5)R1944-R1948(2000) 4.Cavun, S., GÖktalay, G., and Millington, W.R.Glycyl-glutamine, an endogenous β-endorphin-derived peptide, inhibits morphine-induced conditioned place preference, tolerance, dependence, and withdrawalJ. Pharmacol. Exp. Ther.315(2)949-958(2005)