Effects of heat stress on postabsorptive metabolism and energetics.

Environmental-induced hyperthermia compromises efficient animal production and jeopardizes animal welfare. Reduced productive output during heat stress was traditionally thought to result from decreased nutrient intake. Our observations challenge this dogma and indicate that heat-stressed animals employ novel homeorhetic strategies to direct metabolic and fuel selection priorities independent of nutrient intake or energy balance. Alterations in systemic physiology support a shift in carbohydrate metabolism, evident through changes such as basal and stimulated circulating insulin levels. Hepatocyte and myocyte metabolism also show clear differences in glucose production and use during heat stress. Perhaps most intriguing, given the energetic shortfall of the heat-stressed animal, is the apparent lack of fat mobilization from adipose tissue coupled with a reduced responsiveness to lipolytic stimuli. Thus, the heat stress response markedly alters postabsorptive carbohydrate, lipid, and protein metabolism independently of reduced feed intake through coordinated changes in fuel supply and utilization by multiple tissues.