Regional heterogeneity in the processing of pro-opiomelanocortin in rat brain.

The occurrence of alpha-N-acetylated forms of beta-endorphin (beta END) and alpha-melanotropin (alpha MSH) in rat pituitary and brain regions was investigated using high-performance liquid chromatography and radioimmunoassay. Acetylated derivatives of both peptides predominated in neurointermediate pituitary but represented minor components in anterior pituitary, in agreement with previous reports. Regional differences in the degree of acetylation were also observed in brain. Arcuate nucleus, the major source of beta END and alpha MSH in brain, contained small amounts of acetylated forms but most of the immunoreactivity chromatographed with the unmodified beta END 1-31 and des-acetyl-alpha MSH. Amygdala and periaquaductal grey contained the non-acetylated forms only, whereas in nucleus accumbens the major immunoreactive species were the acetylated derivatives of beta END 1-31 and beta END 1-27 along with the mono- and di-acetyl forms of alpha MSH. The selective distribution of acetylated beta END and alpha MSH suggests heterogeneity in the processing of POMC in brain and may indicate a role for alpha-N-acetylation in regulating the biological activities of these peptides in specific brain regions.