Characterization of opioid peptides in guinea-pig heart and skin

Using reverse phase HPLC separations, and assay of eluate fractions in the mouse vas deferens, extracts of heart and skin from guinea-pigs were shown to contain several species of opioid-active material in low amounts (3-20 pmol/g as [Met5]enkephalin). Immunohistochemical studies revealed in the heart a small number of enkephalin-immunoreactive nerve fibres, particularly in cardiac ganglia and some small cells (paraganglionic cells, APUD cells). In the skin, enkephalin-immunoreactivity was confined to Merkel cells. Cardiac and cutaneous opioid peptides may modulate peripheral cardiovascular and sensory functions.