Heat loss and heat production induced by capsaicin.

皮下注射辣椒素(5 mg/kg)可立即使乌拉坦麻醉大鼠尾部皮肤温度升高2小时，提示热损失增加。注射辣椒素后，产热指标耗氧量也立即增加，并持续10h以上。结肠温度在注射后1h内下降，随后持续一段较长的高温期。肾上腺去髓质可显著减弱辣椒素诱导的热产生，而去交感神经对肩峰间棕色脂肪组织(IBAT)有部分作用。然而，辣椒素诱导的热量损失在这些大鼠中是正常的。在皮肤血管扩张最大的大鼠中，辣椒素不会进一步增加热量损失，但正常情况下会诱导热量产生。接下来，我们研究了支配IBAT的辣椒素敏感感觉纤维的功能。将IBAT加热到40-44ﾟ℃会减弱随后的去甲肾上腺素诱导的产热作用。在这个升温范围内，IBAT温度越高，衰减越大。注射5.2nmolCGRP，但不注射P物质或生理盐水，可模拟IBAT的热刺激效应。去IBAT神经或用辣椒素受体拮抗剂辣椒素预处理可阻断辣椒素的作用。我们认为，温度和辣椒素敏感神经纤维释放降钙素基因相关肽，以减轻棕色脂肪细胞的NIT。

Subcutaneous administration of capsaicin (5 mg/kg) immediately increased the temperature of the tail skin for 2 h in urethan-anesthetized rats, suggesting an increase in heat loss. Oxygen consumption, an index of heat production, also immediately increased after the capsaicin injection, and this increase lasted for more than 10 h. Colonic temperature decreased within 1 h after the injection, and this decrease was followed by a long-lasting hyperthermic period. Adrenal demedullation largely attenuated the capsaicin-induced heat production, and sympathetic denervation of the interscapular brown adipose tissue (IBAT) partly did so. However, capsaicin-induced heat loss was normal in these rats. In rats with cutaneous vasodilatation maximized, capsaicin did not further increase heat loss but normally induced heat production. Thus, capsaicin simultaneously activates independent networks for heat loss and heat production.Next, we examined the function of capsaicin-sensitive sensory fibers that innervate IBAT.Warming of the IBAT to 40-44ﾟC attenuated the subsequent noradrenaline-induced thermogenesis (NIT) of the IBAT.In this range of warming, higher IBAT temperatures resulted in more attenuation. Administration of 5.2 nmol CGRP but not substance P or vehicle saline mimicked the effect of thermal stimulation of IBAT.Administration of capsacin (1 mg/kg, s.c.) also attenuated the NIT.Denervation of the IBAT or pretreatment with capsazepine, a capsaicin receptor antagonist, blocked the effect of capsaicin. We propose that temperature- and capsaicin-sensitive nerve fibers release CGRP to attenuate the NIT of brown adipocytes.