Regulation of bioactive β‐endorphin processing in rat pars intermedia

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Abstract
Acid extracts of rat pituitary neuro‐intermediate lobes have been shown by ion‐exchange chromatography and radio‐immunoassay to contain predominantly the inactive derivatives of β‐endorphin, αN‐acetyl β‐eadorphin 1–27 and α,N‐acetyl β‐endorphin 1–26; the biologically active form, β‐endorphin 1–31, is a minor component. In contrast, it was found that β‐endorphin generated in neuro‐intermediate lobe cells in monolayer culture was less processed: the principal peptides related to bioactive β‐endorphin 1–31. When the cultured cells were incubated in the presence of 10−5 M dopamine or 10−6 M α‐ergocryptine there was a marked increase in the degree of proteolysis and acetylation: the processing pattern reverted to that characteristic of the neuro‐intermediate lobe in situ, with α‐N‐acetyl β‐endorphin 1–26 and α,N‐acetyl β‐endorphin 1–27 as the prominent peptides. The results demonstrate that dopaminergic agents can influence the processing of β‐endorphin‐related peptides in rat pars intermedia, indicating a new level at which the bioactivity may be regulated.