Sequential changes in hepatic mRNA abundance and serum concentration of serum amyloid A in cattle with acute inflammation caused by endotoxin

The objective of the present study was to elucidate sequential changes in mRNA abundance of serum amyloid A (SAA) isotypes in endotoxin (ETX) challenge model cattle. Ten healthy cattle were separated to 2 groups: control and ETX groups. Cattle in the ETX group were challenged by 2.5 µg/kg of O111:B4 lipopolysaccharide in 4 ml of autologous serum. Blood samples were withdrawn at pre, 0.5, 1, 2, 4, 8, 12, 24, 48, 72 and 96 hr after ETX challenge. Plasma ETX activity, serum SAA concentrations, mRNA abundance of interleukin (IL)-6, SAA2 and SAA4 in the liver and polymorphonuclear leukocytes were measured. The plasma ETX activity in the ETX group increased at 0.5 hr after the ETX challenge. The serum SAA value remained higher between 12 and 72 hr after the ETX challenge than that of the control group. Hepatic IL-6 mRNA abundance in the ETX group increased at 2 hr after the ETX challenge. Hepatic SAA2 and SAA4 mRNA abundance significantly increased from 4 hr after administration, and remained significantly higher than those pre-values up to 12 and 24 hr, respectively. The abundance ratio of hepatic SAA2 was much higher than that of SAA4. The major isotype was SAA2 in liver tissue, and it is indicating systemic inflammation in cattle.