Thermogenesis of brown adipose tissue in cold-acclimated rats

Multilocular brown adipose tissue in the rat is shown to increase in both mass and respiratory rate, in vitro, during cold acclimation. By vascular convection the resulting heat is directly applied to the thoracocervical regions of the spinal cord, the heart, and other thoracic organs. The vasculature is so arranged as to exercise a fine order of thermogenic control over the brown fat and temperature of the peripheral venous returns to the thorax, facilitated in part by a "reverse" type of countercurrent heat exchange apparently not previously described.