Time course of ROS production in skeletal muscle mitochondria from chronic heat-exposed broiler chicken

This study was designed to elucidate physiological changes of skeletal muscle mitochondria from broiler chickens (Gallus gallus) during chronic heat exposure. Chickens (19-day-old) were exposed to either constant heat stress (34 degrees C) or kept at control temperature (24 degrees C) for 14days. Mitochondrial ROS production for control group showed little changes during the experimental periods, whereas that for the heat-stressed group was increased after 3, 5 and 9days of heat exposure and returned to original levels at day 14. Mitochondrial membrane potential in state 4 for heat-stressed birds was higher than those of control birds after 3 and 5days, but was not at day 14. Mitochondrial oxygen consumption rate in state 3 was increased after 3 and 5days, and also returned to original levels by day 14. These results suggest that chronic heat stress induces increased ROS production in skeletal muscle mitochondria, probably via elevation of the membrane potential in state 4, resulting from enhanced oxygen consumption in the initial stage of heat exposure. These physiological changes were no longer observed at day 14, possibly because the animals had acclimatized to environmental heat stress.