Metabolic Priorities During Heat Stress With An Emphasis on Skeletal Muscle

Abstract

ABSTRACT: Environmental heat stress undermines efficient animal production resulting in a significant financial burden to agricultural producers. The reduction in performance during heat stress is traditionally thought toresult from reduced nutrient intake. Recently, this notion has been challenged with observations indicating heat-stressed animals may exploit novel that homeorhetic strategies to direct metabolic and fuel selection priorities independent of nutrient intake or energy balance. Alterations in systemic physiology support a shift in metabolism, stemming from coordinated interactions at whole-body and tissue-specific levels. Such changes are characterized by increased basal and stimulated circulating insulin concentration, in addition to the ostensible lack of basal adipose tissue lipid mobilization coupled with reduced adipocyte responsiveness to lipolytic stimuli. Hepatic and skeletal muscle cellular bioenergetics also exhibit clear differences in carbohydrate production and use, respectively, due to heat stress. The apparent dichotomy in intermediary metabolism between the 2 tissue types may stem from factors such as rboxylic acid cycletrica substrate flux and mitochondrial respiration. Thus, the heat stress response markedly alters post-absorptive carbohydrate, lipidand protein metabolism , through coordinated changes in fuel supply and utilization across tissues in a manner that is distinct from commonly recognizable changes that occur in animals on a reduced plane of nutrition. Perhaps most intriguing is that the coordinated systemic, cellular, and molecular changes appear conserved across physiological states and amongst different ruminant and monogastric species. Ultimately, these changes result in the reprioritization of skeletal muscle fuel selection during heat stress, which may be important for whole-body metabolism and overall physiological adaptation to hyperthermia.