“…Other peripheral sites of action of the enkephalins include the sympathetic nerves (Gaddis & Dixon, 1982), peripheral vasculature (Sander et al, 1981), adrenal chromaffin cells (Kumakura et al, 1980), baroreceptor reflex activity (Rubin, 1984) or through pulmonary 'JF chemoreceptors (Sapru et al, 1981). Centrally, circulating enkephalins could act on the brain opioid receptors adjacent to the circumventricular regions, areas known to have an incomplete blood-brain barrier (Holaday, 1983;Eulie & Rhee, 1984). Therefore it was of interest to us to study the circulating levels of [Metlenkephalin-like immunoreactivity (MLI) in response to cardiovascular changes.…”