Characterization of N^α-acetyl-α-endorphin from rat neurointermediate lobe and its distribution in pituitary and brain

N^α-Acetyl-α-endorphin was characterized from rat neurointermediate lobe. The distribution of the acetylated and the non-acetylated form of ^α- endorphin in dissected areas of pituitary and brain appeared to be uneven. α-Endorphin appeared to be the main peptide in the anterior pituitary, whereas in the neurointermediate lobe N^α-acetyl-α-endorphin accounted for most of the α-endorphin immunoreactivity. In the brain, the highest concentration of α-endorphin immunoreactivity was found in the hypothalamus. In hypothalamus and thalamus α-endorphin predominated, whereas in amygdala, hippocampus and septum N^α-acetyl-α-endorphin represented most of the α-endorphin-immunoreactivity. In view of the non- opioid properties of acetylated endorphins, it is suggested that acetylation represents a mechanism allowing the organism to specifically select the non-opioid behavioral activities enclosed in the endorphin sequence.