Tissue distribution of cold-induced thermogenesis in conscious warm- or cold-acclimated rats reevaluated from changes in tissue blood flow: the dominant role of brown adipose tissue in the replacement of shivering by nonshivering thermogenesis.

Radioactive microspheres (12–16 μm) were used to measure cardiac output (CO), its fractional distribution, and hence tissue blood flow in conscious, warm-acclimated (WA) or cold-acclimated (CA) white rats exposed to temperatures of 25, 21, 6, −6, and −19 °C, the objective being to assess the tissue distribution of cold-induced thermogenesis. Total oxygen consumption was also measured. CA rats at 25 °C (CA25) had elevated arteriovenous shunting and other signs of heat stress. CA21 proved more suitable controls for the CA group. The cold-induced changes in blood flow to total skeletal muscle not involved in respiratory movements (M) and to the major masses of brown adipose tissue (BAT) were quantitatively very different in the two acclimation groups: in WA25 and CA21 flows to M were 31 (0.24 CO) and 27 (0.17 CO) mL/min, respectively, while flows to BAT were 2.1 and 9.7 mL/min; in WA−19 and CA−19 flows to M were 62 (0.32 CO) and 35 (0.16 CO) mL/min, respectively, while flows to BAT were 25 and 56 mL/min. In ...