Induction of nitric oxide production by bovine mammary epithelial cells and blood leukocytes

A recent study from our laboratory has shown that significant amounts of ni tric oxide are released by somatic cells recovered during endotoxin-induced mastitis. The present study was undertaken to investigate which cell type( s) among milk somatic cell population can produce nitric oxide under inflam matory conditions. Nitric oxide release from mammary epithelial cell lines and from bovine neutrophils and monocytes extracted from blood was measured in response to cytokines and Escherichia coli lipopolysaccharides. An epit helial cell line isolated from bovine mammary gland, FbE cells, was found t o release nitric oxide after exposure to interleukin-1 beta. This nitric ox ide production was completely abolished by addition of L-N-6-(1-iminoethyl) lysine, a potent inducible nitric oxide synthase inhibitor. Bovine monocyt es produced nitric oxide in response to recombinant bovine interferon-gamma alone or in combination with E. coli lipopolysaccharides. In these cells, nitric oxide release was reduced by the addition of inducible nitric oxide synthase inhibitors L-N-6-(1-iminoethyl) lysine and aminoguanidine. Lipopol ysaccharides and recombinant bovine interferon-gamma increased nitric oxide synthase mRNA in neutrophils, but nitric oxide release could not be detect ed under any of the experimental conditions used. These results show that b ovine epithelial cells and mononuclear phagocytes produce nitric oxide unde r inflammatory conditions and suggest that these cell populations are respo nsible for nitric oxide release observed during mastitis.