Nisoli E, Tonello C, Briscini L, Carruba M O
Department of Pharmacology, Chemotherapy, and Medical Toxicology, LITA Ospedale L. Sacco, Milan University, School of Medicine, Italy.
Endocrinology. 1997 Feb;138(2):676-82. doi: 10.1210/endo.138.2.4956.
Exposure of rat brown adipocytes differentiated in culture to norepinephrine (NE) results in the production of nitrites (NO2-), the breakdown product of nitric oxide (NO). This production, which is blocked by actinomycin D1 is directly related to the duration of exposure to and dose of NE. Cytosol from NE-treated brown fat cells, but not from untreated cultures, catalyzed the Ca(2+)-independent conversion of L-arginine to L-citrulline, which could be significantly blocked by the specific nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester. Reverse transcriptase-PCR demonstrates that the addition of NE; selective beta 1-, beta 2-, or beta 3-adrenergic receptor agonists; or agents increasing cAMP production, such as forskolin, to brown adipocytes stimulates inducible NOS (iNOS) messenger RNA, which is present within 4 h after exposure. That iNOS is synthesized in brown fat cells is confirmed by immunoblotting using an antibody to the iNOS of mouse macrophages, Finally, in both brown adipose tissue (BAT) and brown adipocyte preparations from animals exposed to low temperature, iNOS messenger RNA and protein were expressed, and NOS activity was detectable; these findings were unlikely for room temperature-acclimated rats. We conclude that brown fat cells can express an inducible form of NOS similar to the iNOS of macrophages, and that its production is directly dependent on sympathetic activity in physiological conditions. NO generated by stimulation of iNOS in brown adipocytes may represent an important mechanism to modulate different BAT functions, among which is vasodilation of the BAT microcirculation.
将培养分化的大鼠棕色脂肪细胞暴露于去甲肾上腺素（NE）会导致亚硝酸盐（NO2-）的产生，亚硝酸盐是一氧化氮（NO）的分解产物。这种产生受放线菌素D1阻断，且与暴露持续时间和NE剂量直接相关。来自经NE处理的棕色脂肪细胞的胞质溶胶，而非未经处理的培养物的胞质溶胶，催化了L-精氨酸向L-瓜氨酸的不依赖于Ca(2+)的转化，而这可被特异性一氧化氮合酶（NOS）抑制剂NG-硝基-L-精氨酸甲酯显著阻断。逆转录酶-PCR表明，向棕色脂肪细胞中添加NE、选择性β1-、β2-或β3-肾上腺素能受体激动剂，或增加cAMP产生的试剂，如福斯可林，会刺激诱导型NOS（iNOS）信使RNA，其在暴露后4小时内出现。使用针对小鼠巨噬细胞iNOS的抗体进行免疫印迹证实棕色脂肪细胞中合成了iNOS。最后，在暴露于低温的动物的棕色脂肪组织（BAT）和棕色脂肪细胞制剂中，iNOS信使RNA和蛋白均有表达，且可检测到NOS活性；对于适应室温的大鼠，这些发现不太可能出现。我们得出结论，棕色脂肪细胞可表达一种类似于巨噬细胞iNOS的诱导型NOS，且其产生在生理条件下直接依赖于交感神经活动。棕色脂肪细胞中iNOS受刺激产生的NO可能代表一种调节不同BAT功能的重要机制，其中包括BAT微循环的血管舒张。
