Abstract

1. 1. Norepinephrine (NE) levels were measured fluorometrically in brown fat and certain other tissues of normal, cold acclimated, hibernating, and newly aroused hamsters. 2. 2. During cold acclimation the absolute quantity of NE in brown fat increased along with the tissue mass. 3. 3. Brown fat NE decreased significantly in hibernating hamsters. A primed system for accelerated NE turnover, which could be important for arousal thermogenesis, is suggested. 4. 4. NE turnover was estimated in brown fat, heart, and spleen by measuring the NE decline after blockade of NE synthesis with α-methyl- p-tyrosine. 5. 5. Brown fat NE turnover was greater in cold acclimated hamsters (4° C.) than in normal controls (23° C.). This could be important for efficient brown fat thermogenesis during cold exposure. 6. 6. Brown fat NE turnover was increased in both normal controls and cold acclimated hamsters exposed acutely to 4° C. Steady-state NE declined in normal brown fat but not in cold acclimated brown fat during acute cold exposure. This could indicate an increased capacity for NE synthesis as well as turnover in cold acclimated brown fat.

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