Effect of the acute heat stress on serum endotoxin concentration and the expression of TLR4 mRNA in liver of Arbor Acres broiler chickens

Abstract

This study was undertaken to investigate the relationship between gut-derived endotoxin and the Toll-like receptor 4 (TLR4) expression in the liver of broilers under acute heat stress (AHS). For this purpose, 120 Arbor Acres chicks were randomised into two groups: control temperature group (CT group, 22 ± 1°C) and high temperature group (HT group, 38 ± 1°C). The chicks received AHS at Day 28 and their small intestine, liver and blood samples were collected after 2 h, 5 h and 10 h to examine the histopathology, biochemical parameters, endotoxin concentrations and TLR4 expression. The results showed that damaged intestinal villi and severe congestion of the hepatic sinusoids were observed, especially after 10 h of AHS in the HT group. In addition, the levels of alanine transferase, aspartate transaminase, and direct bilirubin, except alkaline phosphataseafter were significantly elevated (P < 0.05) and total bilirubin (P < 0.01) and albumin (P < 0.05) were decreased after 10 h of AHS as compared with the CT group, which are associated with liver function. Moreover, the mRNA expression of TLR4 in the liver was noticeably upregulated (P < 0.05) during AHS with significantly increased in endotoxin concentration (P < 0.01) of broilers. Altogether, these findings suggest that the upregulated expression of TLR4 mRNA was triggered via gut-derived endotoxin in heat stress-induced liver injury.