Heat loss and heat production induced by capsaicin.

皮下注射辣椒素（5毫克/公斤）立即增加温度的尾部皮肤2小时在麻醉大鼠，表明增加热损失。氧消耗，产热的指标，也立即增加后，辣椒素注射，并持续超过10小时。结肠温度在注射后1小时内下降，这种下降之后是一个长期持续的高热期。肾上腺去髓鞘在很大程度上减弱了辣椒素诱导的产热，和交感神经的肩胛间棕色脂肪组织（IBAT）部分做到这一点。然而，辣椒素诱导的热量损失在这些大鼠中是正常的。在皮肤血管舒张最大化的大鼠中，辣椒素没有进一步增加热量损失，但正常诱导产热。因此，辣椒素同时激活独立的热损失和热产生网络。接下来，我们检查了神经支配IBAT的辣椒素敏感感觉纤维的功能。将IBAT升温至40-44 ° C会减弱随后的去甲肾上腺素诱导的IBAT产热（NIT）。在这个范围内变暖，IBAT温度越高，衰减程度越大。施用5.2nmol CGRP而不是P物质或载体盐水模拟IBAT的热刺激的效果。去IBAT神经或辣椒素受体拮抗剂辣椒平预处理可阻断辣椒素的作用。我们建议，温度和辣椒素敏感的神经纤维释放CGRP衰减棕色脂肪细胞的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.