ENKEPHALINS IN ADRENOMEDULLARY CHROMAFFIN CELLS AND SYMPATHETIC NERVES

Publisher Summary This chapter discusses the role of enkephalins in adrenomedullary chromaffin cells and sympathetic nerves. Adrenomedullary secretion is activated as a part of the general psycho-neuroendocrine system that maintains homeostasis and responds to situations of stress and coping. As the mechanism of secretion is exocytosis, all soluble chromaffin vesicle components are released into the circulation; as a consequence, the secretion of catecholamines (CA) should be accompanied by a similar amount (by weight) of vesicular proteins and peptides. While studying the function of these secreted proteins and peptides, it was found that adrenomedullary cells synthesize leu- and met-enkephalin and other opiate-like peptides (OLP). The OLP are stored in the chromaffin vesicles and co-secreted with CA. The initial studies indicated that OLP are also present in the spleen and splenic nerve. The presence of OLP in adrenal medulla and sympathetic neurons has been independently confirmed, and an increasing number of peptides with M 500 to 25,000, containing the leu- and/or met-enkephalin sequence have recently been isolated from the adrenal medulla. The majority of these peptides are only active in the radioreceptor assay or in the radioimmunoassay for enkephalins after tryptic digestion. The studies have been restricted to the peptides immediately active (untrypsinized).