– Acetyl β-endorphin (1-26) is a neuropeptide found in rat hippocampus, brain stem, and pituitary. It is also present in the human hypothalamus, where it comprises approximately 4.9% of total β-endorphin peptides. Acetyl β-endorphin (1-26) is produced through posttranslational processing of β-endorphin and is processed similarly in rat and human hypothalamus. Levels of acetyl β-endorphin (1-26) increase in the rat pars intermedia and brain stem following chronic administration of haloperidol .