Aoki Ken, Stephens Dan P, Zhao Kun, Kosiba Wojciech A, Johnson John M
Department of Physiology, University of Texas Health Science Center, San Antonio, Texas, USA.
Am J Physiol Regul Integr Comp Physiol. 2006 Sep;291(3):R619-24. doi: 10.1152/ajpregu.00117.2006.
In humans, the nocturnal fall in internal temperature is associated with increased endogenous melatonin and with a shift in the thermoregulatory control of skin blood flow (SkBF), suggesting a role for melatonin in the control of SkBF. The purpose of this study was to test whether daytime exogenous melatonin would shift control of SkBF to lower internal temperatures during heat stress, as is seen at night. Healthy male subjects (n = 8) underwent body heating with melatonin administration (Mel) or without (control), in random order at least 1 wk apart. SkBF was monitored at sites pretreated with bretylium to block vasoconstrictor nerve function and at untreated sites. Cutaneous vascular conductance, calculated from SkBF and arterial pressure, sweating rate (SR), and heart rate (HR) were monitored. Skin temperature was elevated to 38 degrees C for 35-50 min. Baseline esophageal temperature (Tes) was lower in Mel than in control (P < 0.01). The Tes threshold for cutaneous vasodilation and the slope of cutaneous vascular conductance with respect to Tes were also lower in Mel at both untreated and bretylium-treated sites (P < 0.05). The Tes threshold for the onset of sweating and the Tes for a standard HR were reduced in Mel. The slope of the relationship of HR, but not SR, to Tes was lower in Mel (P < 0.05). These findings suggest that melatonin affects the thermoregulatory control of SkBF during hyperthermia via the cutaneous active vasodilator system. Because control of SR and HR are also modified, a central action of melatonin is suggested.
在人类中，夜间体内温度下降与内源性褪黑素增加以及皮肤血流量（SkBF）的体温调节控制转变有关，这表明褪黑素在SkBF控制中发挥作用。本研究的目的是测试白天外源性褪黑素是否会像在夜间那样，在热应激期间将SkBF的控制转变为更低的体内温度。健康男性受试者（n = 8）随机接受有褪黑素给药（Mel）或无褪黑素给药（对照）的身体加热，每次至少间隔1周。在预先用溴苄铵处理以阻断血管收缩神经功能的部位和未处理部位监测SkBF。监测由SkBF和动脉压计算得出的皮肤血管传导率、出汗率（SR）和心率（HR）。皮肤温度升高至38摄氏度并持续35 - 50分钟。Mel组的基线食管温度（Tes）低于对照组（P < 0.01）。在未处理部位和经溴苄铵处理部位，Mel组的皮肤血管舒张的Tes阈值以及皮肤血管传导率相对于Tes的斜率也较低（P < 0.05）。Mel组出汗开始的Tes阈值和标准HR对应的Tes降低。Mel组中HR与Tes关系的斜率降低，但SR与Tes关系的斜率未降低（P < 0.05）。这些发现表明，褪黑素在热疗期间通过皮肤活性血管舒张系统影响SkBF的体温调节控制。由于SR和HR的控制也发生了改变，提示褪黑素存在中枢作用。
