Non-shivering Thermogenesis and Brown Adipose Tissue in the Human New-born Infant

Abstract

WHEN new-born rabbits are exposed to cold or infused with physiological amounts of noradrenaline, there is a substantial increase in O₂ consumption without shivering¹. Recently, local heat production has been demonstrated in the large mass of brown adipose tissue found in the interscapular region in the newborn rabbit². Removal of brown adipose tissue abolishes the increase in O₂ consumption on exposure to cold or infusion of noradrenaline³. Heat production is accompanied by a four-fold rise in plasma glycerol and a barely significant rise in plasma-free fatty acids⁴. Since brown adipose tissue has no glycerol kinase this rise in plasma glycerol is an indication of lipolysis of triglycerides⁴. The small rise in plasma-free fatty acids suggests that fatty acids are being oxidized locally in brown adipose tissue, with the production of heat. Brown adipose tissue is a very rich source of oxidative enzymes⁵ and co-enzymes⁶ and in the new-born rabbit has an in vitro O₂ consumption higher even than that of cardiac muscle⁴.