1. A direct method for measuring venous outflow from brown adipose tissue in anaesthetized new-born rabbits is described.2. During noradrenaline infusion the mean blood flow through brown adipose tissue increased from 87 to 360 ml./100 g tissue (wet wt.).min, and the mean rate of oxygen consumption of brown adipose tissue rose from 9·3 to 60 ml. O2/100 g tissue.min.3. During cold exposure the mean blood flow through brown adipose tissue increased from 90 to 304 ml./100 g tissue.min.4. The mean cardiac output was 266 ml./kg body weight.min; during noradrenaline infusion it was 405 ml./kg body weight.min. At rest about one tenth, and during noradrenaline infusion about one quarter of the cardiac output went to brown adipose tissue.5. It was calculated that most of the extra oxygen consumed during the metabolic response of the anaesthetized new-born rabbit to noradrenaline infusion or cold exposure was consumed by brown adipose tissue.6. Hypoxia (breathing 10% O2 in N2) greatly reduced the increase in oxygen consumption but not the increase in blood flow in brown adipose tissue caused by noradrenaline infusion.
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