Abstract
Adrenal medulla has recently been shown to contain high concentrations of enkephalin immunoreactive peptides. In the present study, we report the levels of Methionine-Enkephalin (M-ENK) and Leucine-Enkephalin (L-ENK) in extracts from six cases of human pheochromocytoma. The molecular forms of M-ENK have been characterized by gel filtration chromatography. PRO-M-ENK mRNA extracted from one tumour has been estimated to represent 1% of total mRNA after in vitro translation. M-ENK immunoreactive peptides are secreted in the culture medium of dispersed cultured cells of human pheochromocytoma. This secretion is stimulated when nicotine (10 −5 M) is added to the medium. Nicotinic stimulation is inhibited by fentanyl (10 −5 M) or clonidine (10 −4 M). However, the level of plasma M-ENK in pheochromocytoma patients is not significantly different from normal patients. Data from Faden and Holaday (1) have established that naloxone (an opiate antagonist) a beneficial role in shock, but the origin and meaning of plasma M-ENK remain to be established.
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