Effect of Acute Heat Stress on Heat Shock Protein 70 and Its Corresponding mRNA Expression in the Heart, Liver, and Kidney of Broilers

The objective of this study was to investigate the expression and localization of heat shock protein 70 (Hsp70) and its mRNA in the heart, liver, and kidney of acutely heat-stressed broilers at various stressing times. Male AA broilers (n = 100) were randomly divided into 5 groups of 20 birds per group. After 30 d of adaptive feeding at ambient temperature, 80 experimental broilers were suddenly heat stressed by increasing the environmental temperature from $22{\pm}1^{\circ}C$ to $37{\pm}1^{\circ}C$. The 4 groups were heat stressed for 2, 3, 5, and 10 h, respectively. The localizations of Hsp70 protein and mRNA, determined by immunohistochemical staining and in situ hybridization, respectively, were demonstrated to be tissue dependent, implying that different tissues have differential sensibilities to heat stress. Intense Hsp70 staining was identified in the vascular endothelial cell of heart, liver and kidney, suggesting an association between expression of Hsp70 in vascular endothelial cell and functional recovery of blood vessels after heat shock treatment. Ante-mortem heat stress had a significant effect on the expression of Hsp70 protein and mRNA. The quantitation of Hsp70 protein and mRNA were both time and tissue dependent. During the exposure to heat stress, the heart, liver and kidney of broiler chickens exhibited increased amounts of Hsp70 protein and mRNA. The expression of hsp70 mRNA in the heart, liver and kidney of heat-stressed broilers increased significantly and attained the highest level after a 2-h exposure to elevated temperatures. However, significant elevations in Hsp70 protein occurred after 2, 5, and 3 h of heat stressing, respectively, indicating that the stress-induced responses vary among different tissues.