Barbital-sedated, warm-acclimated (WA) or cold-acclimated (CA) rats were infused intravenously with noradenaline (NA) at doses of 0, 2.5, 5.0, and 10 ng min−1 g−0.74 body weight during a period of 30 min. Concentration of NA in arterial plasma, O2 consumption. and rectal temperature were measured before, during, and after NA infusion. Upon infusion of NA, plasma NA increased rapidly to a plateau level which was directly related to the dose infused. However, for each dose, the level was much lower in CA than in WA rats. In both WA and CA rats the increase in O2 consumption above the preinfusion rate was linearly related to the increase in the concentration of plasma NA, but the increase in O2 consumption with each dose was greater in CA than in WA rats. Thus, the slope of the relation between increase in O2 consumption and increase in plasma NA was greater by 4.7 times in CA than in WA rats. Differences in calorigenic response to circulating NA are attributed to a greater amount of brown adipose tissue (BAT) and to a higher calorigenic capacity per gram of this tissue in CA that in WA rats. The molar concentrations of circulating NA which stimulated calorigenesis in the intact white rat are in the same range (from 10−9 to 10−7 M) as those reported by others to stimulate O2 consumption of isolated hamster brown adipocytes and of perifused rat BAT fragments. It is suggested that circulating levels of NA which are effective in stimulating calorigenesis in the intact animal approximate average synaptic concentrations of NA in calorigenic effectors during noradrenergic nerve stimulation resulting from cold exposure.
No takes yet. Share an insight, caveat, or question.
Depocas et al. (1978) studied this question.