Young J B, Saville E, Rothwell N J, Stock M J, Landsberg L
J Clin Invest. 1982 May;69(5):1061-71. doi: 10.1172/jci110541.
Brown adipose tissue (BAT) is an important site of adaptive changes in thermogenesis in the rat. The sympathetic nervous system, which richly supplies BAT, is thought to play an important role in the regulation of BAT thermogenesis because catecholamines stimulate and beta adrenergic blocking agents inhibit oxygen consumption in this tissue. The present studies were carried out to assess directly sympathetic activity in BAT in response to cold exposure and to changes in dietary intake, both of which alter heat production in the rat. Sympathetic activity was determined from the rate of norepinephrine (NE) turnover in interscapular brown adipose tissue (IBAT) after preliminary experiments validated the use of NE turnover techniques in IBAT. Acute exposure to 4 degrees C increased NE turnover in IBAT 4- to 12-fold compared with ambient temperature controls, depending upon the interval over which the turnover measurement was made, while in the heart NE turnover doubled in response to the same cold stimulus. In animals exposed to cold continuously for 10 d before study, NE turnover measurements in IBAT and in the heart were elevated comparably to those obtained during acute exposure. Alterations in feeding were also associated with changes in NE turnover in IBAT. Fasting for 2 d decreased NE turnover in IBAT (-35% from 29.2+/-4.2 ng NE/h to 18.9+/-5.9) and in heart (-52%). In animals fed a "cafeteria" diet, a model of voluntary overfeeding in the rat, NE turnover was increased in both IBAT (+108% from 24.8+/-4.5 ng NE/h to 51.7+/-6.8) and heart (+66%). Because ganglionic blockade exerted a greater effect on NE turnover in IBAT in cafeteria-fed rats than in controls, the increase in NE turnover in IBAT with this overfeeding regimen reflects enhanced central sympathetic outflow. Thus NE turnover techniques can be satisfactorily applied to the assessment of sympathetic nervous system activity in IBAT. The experiments reported here demonstrate changes in sympathetic activity in IBAT that parallel known adaptive changes in heat production in the rat. These studies, therefore, support the concept that the increased thermogenesis of chronic cold exposure and of cafeteria feeding occur by similar mechanisms and imply an important role for the sympathetic nervous system, mediated in part through BAT, in the regulation of energy balance in the rat.
棕色脂肪组织（BAT）是大鼠产热适应性变化的重要部位。丰富支配BAT的交感神经系统被认为在BAT产热调节中起重要作用，因为儿茶酚胺刺激该组织耗氧，而β肾上腺素能阻滞剂抑制其耗氧。本研究旨在直接评估BAT对冷暴露和饮食摄入量变化的交感神经活动，这两者均会改变大鼠的产热。在初步实验验证了去甲肾上腺素（NE）周转技术可用于肩胛间棕色脂肪组织（IBAT）后，通过测定IBAT中NE的周转速率来确定交感神经活动。与环境温度对照组相比，急性暴露于4℃使IBAT中的NE周转增加了4至12倍，这取决于周转测量的时间间隔，而相同的冷刺激使心脏中的NE周转增加了一倍。在研究前连续10天暴露于寒冷的动物中，IBAT和心脏中的NE周转测量值与急性暴露期间获得的值相当。饮食改变也与IBAT中NE周转的变化有关。禁食2天使IBAT中的NE周转减少（从29.2±4.2 ng NE/h降至18.9±5.9，下降35%），心脏中的NE周转减少52%。在喂食“自助餐”饮食（大鼠自愿过度进食的模型）的动物中，IBAT和心脏中的NE周转均增加（IBAT从24.8±4.5 ng NE/h增加108%至51.7±6.8，心脏增加66%）。由于神经节阻断对喂食自助餐大鼠的IBAT中NE周转的影响比对对照组的影响更大，因此这种过度喂养方案使IBAT中NE周转增加反映了中枢交感神经输出增强。因此，NE周转技术可令人满意地应用于评估IBAT中的交感神经系统活动。此处报道的实验表明，IBAT中的交感神经活动变化与大鼠已知的产热适应性变化平行。因此，这些研究支持这样的概念，即慢性冷暴露和自助餐喂养导致的产热增加通过相似机制发生，并暗示交感神经系统在大鼠能量平衡调节中起重要作用，部分通过BAT介导。
