METABOLIC CHANGES ASSOCIATED WITH SUSTAINED 48-HR SHIVERING THERMOGENESIS IN THE NEWBORN PIG

Metabolic changes associated with sustained 48-hr shivering thermogene sis were studied in piglets maintained at 34 (thermoneutrality) or 25 degrees C (cold) between 6 and 54 hr of life. Despite their high shive ring activity and elevated heat production, cold-exposed piglets exhib ited a slightly lower rectal temperature than thermoneutral animals (- 1.1 degrees C; P < 0.01) at the end of the treatment. The enhancement of heat production and shivering activity were associated with a decre ase in muscle glycogen (-47%; P < 0.05) and total lipid content (-23%; P < 0.05), a reduction of blood lactate levels (P < 0.05) and an enha ncement of muscle cytochrome oxidase activity (+20%; P < 0.05), which suggests that muscle oxidative potential was increased by cold exposur e. Potential for capturing lipids (lipoprotein lipase activity) was al so higher in the red rhomboideus muscle (+71%; P < 0.01) and lower in adipose tissue (-58%; P < 0.01) of the cold-exposed piglets. Measureme nts performed at the mitochondrial level show no changes in rhomboideu s muscle, but respiratory capacities (state IV and FCCP-stimulated res piration) and intermyofibrillar mitochondria oxidative and phosphoryla tive (creatinine kinase activity) capacities were enhanced in longissi mus dorsi muscle (P < 0.05). These changes may contribute to provide m uscles with nonlimiting amount of readily oxidable substrates and ATP necessary for shivering thermogenesis. A rise in plasma norepinephrine levels was also observed during the second day of cold exposure (P < 0.05).