Effect of Heat Stress on the Expression of HSP70, UCP3 and CYP450 Genes in Liver; Longissimus Dorsi and Semitendinosus Muscle of Growing Pigs

High Ambient Temperature (AT) provokes Heat Stress (HS) in animals, which is characterized by increased body temperature, Reactive Oxygen Species (ROS) production and cell damage. Uncoupling Proteins (UCP) may contribute to dissipate body heat, cytochrome P450 (CYP3A4) reduces ROS and Heat Shock Proteins (HSP) prevent protein denaturalization. This study analyzed the expression of HSP70, UCP3 and CYP3A in liver, Longissimus Dorsi (LD) and Semitendinosus (ST) muscles of pigs exposed to HS conditions. A 21-d experiment was conducted with 18 pigs (32.6±3.2 kg body weight) divided into 3 treatments: (1) HS, pigs exposed to natural AT (29.5-37.2°C) fed ad libitum; (2) TNad, thermoneutral conditions (24.0±2.0°C) fed ad libitum; (3) TNpf, thermoneutral fed same amount as HS pigs. Hepatic expression of HSP70 in HS pigs was 4-fold higher than in TNad pigs (p=0.039); no differences were observed between HS and TNpf, or between TNad and TNpf pigs (p>0.10). There were no differences in HSP70 expression in both muscles (p>0.10) because of HS or feed intake. Expression of UCP3 in LD and ST did not differ (p>0.10) between treatments; neither the expression of CYP3A in liver was affected by HS, or feed intake level (p>0.10). Apparently, pigs became adapted to HS because expression of mitochondrial UCP3 and CYP3A was not affected after 21 d of HS exposure and the increased HSP70 expression in liver could have helped cells to maintain their proteins integrity.