Chromaffin cell epinephrine secretion mediated by a macrophage peptide: the role of endotoxin.
Recent studies show that mononuclear cells release a small peptide (molecular weight < 3,000) that stimulates chromaffin cell epinephrine secretion (1). The present study demonstrates that endotoxin (ETX) enhances this mononuclear cell-mediated epinephrine secretion and examines the potential mechanism for regulation of this peptide. Mononuclear cells from bovine spleen were cultured 24 h in serum-free media after which the supernatant (conditioned media, CM) was harvested and filtered to remove molecules with a molecular weight greater than 3,000. In vitro epinephrine secretion from bovine chromaffin cells was used as a test system and CM-secretion expressed as a percentage of total cell content. ETX challenge (1 microgram/mL) of mononuclear cell cultures significantly enhanced bioactivity of CM (control-CM = 11.8 +/- .7, ETX-CM = 17.7 +/- 2.8). Separation of cell populations by adherence to plastic revealed that T cell and/or B cell populations were the main source of the bioactive peptide(s) in unstimulated cell cultures (T/B cell = 12.9 +/- .7, M phi = 6.2 +/- .8). In contrast, ETX induced significant bioactive peptide release from the macrophage population (M phi = 6.2 +/- .8, ETX-M phi = 15.9 +/- 2.8). Polyacrylamide gel analysis revealed a small peptide in nonadherent cell CM that was present only in ETX-challenged macrophage cultures. Additionally, data are presented that demonstrate a correlation between CM bioactivity and protease activity in CM. Proteases secreted from mononuclear cells in response to ETX is hypothesized to cleave the bioactive peptide from a larger "parent" protein. This peptide may play a role in the elevation of plasma catecholamines observed in the setting of critical injury and illness and contribute to development of the systemic inflammatory response syndrome (SIRS) and subsequent shock states.
Roberts
J C
JC
Department of Physiology, Loyola University Medical Center, Maywood, Illinois 60153, USA.
Jones
S B
SB
D000818:Animals; D002417:Cattle; D019439:Chromaffin Cells / Q000378:metabolism*; D017077:Culture Media, Conditioned; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D004731:Endotoxins / Q000737:chemistry / Q000494:pharmacology*; D004837:Epinephrine / Q000378:metabolism*; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D007931:Leucyl Aminopeptidase / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000502:physiology; D008264:Macrophages / Q000502:physiology*; D010455:Peptides / Q000737:chemistry / Q000502:physiology*; D010835:Phytohemagglutinins / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D012967:Sodium Dodecyl Sulfate
D017077:Culture Media, Conditioned; D004731:Endotoxins; D010455:Peptides; D010835:Phytohemagglutinins; D011480:Protease Inhibitors; D012967:Sodium Dodecyl Sulfate; D007931:Leucyl Aminopeptidase; D007930:Leucine; C012211:ubenimex; D004837:Epinephrine