The effects of aging on molecular forms of beta- and gamma-endorphins in rat hypothalamus

The influence of aging on the molecular forms of endorphins in the hypothalamus of rats was investigated. Extracts of individual hypothalami from 8- and 24-month-old male Fischer 344 rats were subjected to high-performance liquid chromatography. Eluate fractions were assayed for beta-endorphin-like immunoreactivity (beta E-LI) and gamma-endorphin-like immunoreactivity (gamma E-LI). Hypothalami from adult (8-month-old) rats contained predominantly beta-endorphin-1-31 with smaller amounts of beta-endorphin-1-27 and 1-26. Only 5% of the beta E-LI co-eluted with alpha-N-acetylated forms of beta-endorphin. In hypothalamic extracts from old rats more than 30% of the beta E-LI co-eluted with acetylated forms of beta-endorphin and over 35% of the beta E-LI co-eluted with acetylated or unacetylated beta-endorphin-1-26. The individual elution profiles of beta E-LI were also much more variable among the old rats than among the adult rats. More than 80% of the gamma E-LI from adult rat extracts co-eluted with gamma-endorphin (beta-endorphin-1-17) and less than 3% with alpha-N-acetyl-gamma-endorphin. In contrast, more than 35% of the gamma E-LI from old rat hypothalami was present in the acetylated form. These results suggest that significant alterations in post-translational processing of peptides may occur in neuropeptide systems during aging.