Glucocorticoids inhibit endorphin synthesis by pituitary cells

Abstract

ENDORPHINS in the pituitary gland^1,2 are specifically localised in the intermediate and anterior lobes^3,4, whereas the posterior lobe contains much less opioid activity⁴. Recent results have indicated that β-endorphin and adrenocorticotropic hormone (ACTH) are synthesised by pituitary cells from a common precursor polypeptide^5–8 and that they both appear in the circulation after stressful stimulation⁹. It is well known that an increased potassium concentration stimulates the release of ACTH from pituitary cells in a calcium-dependent fashion¹⁰. Similar potassium-evoked release of endorphins was indicated in AtT/20 cells which originated in the anterior lobe of mouse pituitary tumours¹¹. In addition, a basal release of endorphins was indicated, suggesting a possible dual regulation of endorphin secretion from the pituitary¹¹. Coordinated release of ACTH, β-endorphin and β-lipotropin was reported¹² while the present study was in progress. This study was undertaken to determine whether glucocorticoid hormones, which are known to regulate ACTH, also regulate pituitary endorphins. Although it has recently been shown⁹ that dexamethasone inhibits in vivo elevation of the content of pituitary endorphins after adrenalectomy, the mechanism of the action of this synthetic glucocorticoid remains unclear. Here, we describe data suggesting a direct inhibitory role of glucocorticoids in the synthesis of endorphins by pituitary cells.