Synthesis of enkephalins by adrenal medullary chromaffin cells: reserpine increases incorporation of radiolabeled amino acids.

Adrenal medullary chromaffin cells maintained in a chemically defined, serum-free medium retain high levels of both catecholamines and opiate-like peptides. At least 25% of the opioid activity as measured by radioreceptor assay is present as [Met]- and [Leu]enkephalin. Incubation of chromaffin cells with [3H]tyrosine and [35S]methionine for 3 days results in incorporation of 3H and 35S into [Met]enkephalin and 3H incorporation into [Leu]enkephalin, demonstrating de novo enkephalin synthesis. Addition of 100 nM reserpine to the culture medium causes an 80% depletion of catecholamines and a 100% increase in opioid peptide content 3-4 days later. [Met]Enkephalin content is preferentially induced (290% above control) compared with [Leu]enkephalin (70%) Reserpine increases the fractional radiolabeling of [Met]- and [Leu]enkephalin in excess of control cultures, suggesting that the increase in opiate-like peptides results from an increased rate of synthesis rather than decreased degradation, decreased secretion, or increased processing of preformed precursor(s).