Stress‐Related Changes in β‐Endorphin Processing: The Limitations of Slaughterhouse Material

In the sheep, unlike many other species, a significant proportion (>25%) of immunoreactive β‐endorphin in the anterior pituitary is post‐translationally modified to opioid‐inactive, α‐N‐acetylated forms. In a study to determine the precise molecular nature of α‐N‐acetylated β‐endorphin immunoreactivity, we noted a striking difference in high‐performance liquid chromatography profiles of anterior pituitary extracts between sheep killed on the farm, and age‐, sex‐ and strain‐matched slaughterhouse animals. These altered patterns of a‐N‐acetylated β‐endorphin processing were reproduced in farm animals by chronic (≤ 4 days) treatment with the synthetic glucocorticoid dexamethasone; in contrast dexamethasone had no effect on a‐N‐acetylated β‐endorphin processing in hypothalamo‐pituitary disconnected sheep. These data suggest that (1) the change in processing is a stress response, mediated by prolonged glucocorticoid exposure, (2) this effect is central, rather than a direct effect on the pituitary, and (3) the relative abundance of various peptide sequences in slaughterhouse‐derived material may not reflect their abundance under more physiological conditions.