Wang L C, Anholt E C
J Appl Physiol Respir Environ Exerc Physiol. 1982 Jul;53(1):16-20. doi: 10.1152/jappl.1982.53.1.16.
Previous studies in rats indicate that maximal thermogenesis during severe cold exposure is suppressed by overnight fasting. Since fasting depresses sympathetic activity and the activity of adrenergic receptors, both of which affect substrate mobilization in cold, the present study attempted to restore maximal thermogenesis in fasted rats by exogenous sympathomimetics and a hypoxanthine (aminophylline). In overnight-fasted rats, exogenous sympathomimetics had no effect in further enhancing maximal thermogenesis induced by exposure to severe cold (in He-O2 at -10 degrees C), indicating maximization of endogenous sympathetic discharge and saturation of adrenergic receptor binding during severe cold exposure. In contrast, aminophylline (1.25-37.5 mg/kg ip) elicited "supramaximal thermogenesis" beyond control maximums in both fasted (+19.4%) and fed +14.4%) conditions in a dose-dependent manner, resulting in improved cold tolerance and prevention of hypothermia. Since aminophylline acts distally to adrenergic receptors to increase intracellular adenosine 3',5'-cyclic monophosphate concentration, it is possible that such increases could enhance substrate mobilization to support supramaximal thermogenesis in severe cold.
先前对大鼠的研究表明，严重冷暴露期间的最大产热会因过夜禁食而受到抑制。由于禁食会抑制交感神经活动和肾上腺素能受体的活性，而这两者都会影响寒冷环境下的底物动员，因此本研究试图通过外源性拟交感神经药和一种次黄嘌呤（氨茶碱）来恢复禁食大鼠的最大产热。在过夜禁食的大鼠中，外源性拟交感神经药对进一步增强暴露于严重寒冷环境（在-10℃的氦氧混合气中）所诱导的最大产热没有作用，这表明在严重冷暴露期间内源性交感神经放电已达到最大值且肾上腺素能受体结合已饱和。相比之下，氨茶碱（1.25 - 37.5毫克/千克，腹腔注射）在禁食（增加19.4%）和进食（增加14.4%）的情况下均以剂量依赖的方式引发了超过对照最大值的“超最大产热”，从而提高了耐寒性并预防了体温过低。由于氨茶碱在肾上腺素能受体的下游起作用以增加细胞内3',5'-环磷酸腺苷的浓度，因此这种增加有可能增强底物动员以支持严重寒冷环境下的超最大产热。
