Expression of β-endorphin in peripheral tissues after systemic administration of lipopolysaccharide as a model of endotoxic shock in mice.

BACKGROUND: Endogenous β-endorphin is delivered exclusively from the pituitary gland in various stressful conditions and plays an essential role in the nervous system. Recently, a few studies demonstrated peripheral endogenous opioid secretion from immune cells at inflammatory sites. Here, we investigated the expression of β-endorphin, the most powerful endogenous opioid peptide, in peripheral tissues in response to systemic administration of lipopolysaccharide in mice.

METHODS: Male C57BL/6N mice received intravenously administered lipopolysaccharide to induce an endotoxic shock-like condition. mRNA for proopiomelanocortin, a precursor of β-endorphin, was quantified in peripheral blood cells, liver and spleen. β-endorphin peptide was measured in the liver and spleen.

RESULTS: Expression of proopiomelanocortin mRNA was detected in peripheral tissues after systemic administration of lipopolysaccharide. Lipopolysaccharide also induced β-endorphin expression in the liver and spleen.

CONCLUSION: Expression of proopiomelanocortin mRNA and β-endorphin was detected in peripheral tissues after systemic administration of lipopolysaccharide. These results provide new evidence that peripheral endogenous opioids can be produced not only as a result of local inflammation but also by severe systemic stress such as endotoxic shock. Further study is required to clarify the role of peripheral β-endorphin during endotoxic shock.