Physiological responses and brain oxidative stress in heat exposed growing chickens

Abstract

This study was designed to elucidate physiological responses and time-course change in hydroxyl radical in the brain of chickens exposed to high ambient temperature. Twenty-one-day-old growing chickens were exposed to 34°C for 8 h. The extent of lipid peroxidation and plasma metabolites were investigated before and after 4 and 8 h of heat exposure. Moreover, to study hydroxyl radical (OH) production during heat stress, 4-hydroxybenzoic acid (4-HBA) was perfused as a trapping agent in the lateral ventricle (LV) of chickens. The product of the reaction of 4-HBA with OH, 3, 4-dihydroxybenzoic acid (DHBA), was collected using in vivo microdialysis techniques and analyzed by HPLC. Suppression of food intake was observed in the heat treatment (HT) group at 3 to until 7 h. Rectal temperature was significantly increased at 2 h by acute heat exposure, and the difference between the HT and CT groups was maintained at each time point until the end of the experiment. The plasma MDA concentration and corticosterone were intended to increase at 4 and 8 h in the HT group, but no significant difference was observed. The concentration of uric acid was significantly lower in the HT than CT group at 4 h and 8 h (P<0.05). Calcium, total cholesterol, total protein, and GOT were tended to increase at 4 h and 8 h in the HT group, but no significant difference observed in comparison with the CT group. Local perfusion of 4-HBA in the chicken LV increased extracellular levels of 3, 4-DHBA in the HT group compared with baseline. The significantly increased level of 3, 4-DHBA was observed at 4 h and continued to increase until the end of the experiment. These results indicate that brain oxidative stress should be considered as part of the stress response of growing chickens to heat exposure.