Enkephalin and neuropeptide Y: two colocalized neuropeptides are independently regulated in primary cultures of bovine chromaffin cells.

We have found that Neuropeptide Y is colocalized with enkephalin in bovine adrenal chromaffin cells. The two peptides can be found in the same granules in those cells where they coexist. These cells correspond to the adrenergic subpopulation of chromaffin cells since they contain the epinephrine synthetic enzyme, phenylethanolamine N-methyltransferase. Despite their coexistence, production of the two peptides is independently regulated. Enkephalin levels are doubled after nicotinic depolarization (which increases enkephalin synthesis) or after treatment with reserpine (which increases enkephalin precursor processing). Neither of these treatments, acting by different mechanisms, has any effect on the levels of Neuropeptide Y.