Induction of Nitric Oxide Production by Bovine Mammary Epithelial Cells and Blood Leukocytes

¹ Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, P.O. Box 90, 2000 Route 108 East, Lennoxville, Quebec, J1M 1Z3, Canada
² Department of Animal Science, McGill University, 21 111 Lakeshore Rd, Ste-Anne de Bellevue, Quebec, H9X 3V9, Canada

A recent study from our laboratory has shown that significant amounts of nitric 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 inflammatory 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 epithelial cell line isolated from bovine mammary gland, FbE cells, was found to release nitric oxide after exposure to interleukin-1ß. This nitric oxide production was completely abolished by addition of L-N⁶-(1-iminoethyl) lysine, a potent inducible nitric oxide synthase inhibitor. Bovine monocytes produced nitric oxide in response to recombinant bovine interferon- 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-N⁶-(1-iminoethyl) lysine and aminoguanidine. Lipopolysaccharides and recombinant bovine interferon- increased nitric oxide synthase mRNA in neutrophils, but nitric oxide release could not be detected under any of the experimental conditions used. These results show that bovine epithelial cells and mononuclear phagocytes produce nitric oxide under inflammatory conditions and suggest that these cell populations are responsible for nitric oxide release observed during mastitis.

Key Words: nitric oxide • somatic cells • mastitis • inducible nitric oxide synthase

Submitted on October 30, 2000
Accepted on February 4, 2001

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