Potential immunological influences on peripheral catecholamine secretion were investigated by measuring epinephrine secretion from chromaffin cells in vitro in response to cell-free conditioned media from mononuclear cells. Chromaffin cells were isolated from bovine adrenals whereas mononuclear cells were isolated from bovine spleen tissue or whole bovine blood. In secretion experiments epinephrine release and epinephrine remaining in cells was determined such that secretion was expressed as % of total cell content. After 90 minutes exposure to conditioned media, 22.8 +/- 1.1% of content was released compared to 1.7 +/- 0.2% with RPMI media. Secretion after filtration (< 3,000 MW cutoff) was 21.6 +/- 0.9% whereas after boiling and boiling in acid, secretion was 10.2 +/- 0.2 and 4.3 +/- 0.1% respectively. Dialysis (< 3,000 MW cutoff) reduced the 90 min conditioned media-stimulated epinephrine secretion from 22.5 +/- 3.8% to 2.3 +/- 0.3%. Neither atropine nor hexamethonium blockade altered the conditioned media-stimulated epinephrine secretion. These results suggest that mononuclear cells produce a low molecular weight substance--most likely a peptide--that contributes to the stimulation of epinephrine secretion.