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

Abstract

In the sheep, unlike many other species, a significant proportion ( > 25%) of immunoreactive P-endorphin in the anterior pituitary is post-translationally modified to opioid-inactive, a-N-acetylated forms. In a study to determine the precise molecular nature of a-Nacetylated P-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 P-endorphin processing were reproduced in farm animals by chronic ( 5 4 days) treatment with the synthetic glucocorticoid dexamethasone; in contrast dexamethasone had no effect on a-N-acetylated 8-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 t h a n a direct effect on t h e pituitary, and (3) t h e relative abundance of various peptide sequences in slaughterhouse-derived material may not reflect their abundance under more physiological conditions.The stress-induced release of adrenocorticotropin (ACTH), Pendorphin (PEP), P-lipotropin (PLPH) and other proopiomelanocortin (P0MC)-derived peptides from the anterior pituitary (AP) I \ mediated by hypothalamic-releasing factors secreted into the hypophyseal portal blood system. Synthesis of POMC, and release of processed POMC-derived peptides, are stimulated by both corticotropin-releasing factor (CRF) and arginine vasopresb i n , with other hypothalamic agents possibly involved (1). The AP corticotrope is also subject to inhibitory control by direct glucocorticoid feedback from the adrenal gland (2-4). Glucocorticoids not only inhibit ACTH/BEP release, but also negatively regulate I'OMC gene expression in the AP (5-7). In addition, the synthetic glucocorticoid dexamethasone administered in vivo causes a rapid decrease in C R F content of rat median eminence (8), evidence that glucocorticoids regulate release of POMC products from the AP b y central as well as direct effects. Finally, in addition to regulating biosynthesis of POMC and secretion of its products, glucocorticoids and CRF in vitro (9) have been shown to modulate the pattern of POMC processing in cultured rat AP cells.In the AP of the sheep, in contrast to the rat, a significant proportion ( > 25%) of PEP is a-N-acetylated; that this does not represent intermediate lobe contamination has been shown by \\edge dissection of the neurointermediate lobe, and confirmed by immunocytochemistry (10). The present study was initially undertaken to characterize the precise molecular species of immunoreactive a-N-acetylated endorphin (NacEP) in sheep AP extracts.The immunoreactive profiles, determined by reversed-phase (RP) HPLC and RIA specific for the a-N-acetylated NH, terminus of PEP, differed quite markedly in farm sheep from those observed in age-, sex-and strain-matched slaughterhouse anim...

Identification and Characterization of an Amidating Enzyme in Ovine Heart

“…The expression of both peptide hormones and the enzymes involved in their synthesis is potentially subject to physiological regulation, for example, by glucocorticoids (Smith et al 1989). Indeed, atrial and particularly ventricular ANP expression is increased both in vitro and in vivo by dexamethasone treatment (Needleman et al 1989).…”

“…The present study examines the distribution of PAM activity in the heart of another species, the sheep, which given the availability of abattoir material may prove more useful than the rat in the purification of an atrial amidated peptide. In addition, since tissue levels of several peptide processing enzymes have been shown to be altered by corticosteroids (Smith et al 1989), the potential regulation of cardiac PAM activity in sheep by chronic glucocorticoid administration has been examined.…”