Effect of dietary carbohydrate and phenotype on thyroid hormones and brown adipose tissue locularity in adult LA/N –cp rats

Abstract 1. Groups of lean and corpulent LA/N-cp rats were fed isoenergetic diets containing, 54% carbohydrate as maize starch (MS) or sucrose (SU), 20% protein, 16% mixed fats, plus other essential nutrients and fiber from 1.5–9 months of age. Final body weights of corpulent rats were 2–3 times those of their lean littermates, and were greater with SU than MS diet in both phenotypes. 2. Interscapular brown adipose tissue (IBAT) mass was greater in corpulent than lean and was greater with SU than MS diet in lean but not corpulent rats. IBAT cell diameters and adipocyte volumes were generally similar in both phenotypes, and were not markedly affected by dietary carbohydrate type. 3. Brown adipocyte locularity profiles were qualitatively similar in both phenotypes, and were morphologically indicative of thermogenic activity in both phenotypes. Locule profiles of corpulent animals contained a greater proportion of thermogenically less active types IV and V brown adipocytes than similarly fed lean animals, however, and locule distribution profiles were not influenced by diet. . 4. Serum T3 concentrations were similar in both phenotypes, were greater in SU than MS lean rats and were not influenced by diet in the corpulent phenotype. In contrast, serum thyroxine concentrations and percent thyroxine uptake were not influenced by diet or phenotype. 5. These results are consistent with a partial impairment in BAT-mediated thermogenic activity in the corpulent phenotype and suggest that obesity in this strain may be due to factors other than biochemically defective brown adipose tissue thermogenesis.

摘要 1. 将瘦型与肥胖型LA/N-cp大鼠分为两组，自1.5月龄至9月龄饲喂等能日粮，日粮中54%的碳水化合物分别为玉米淀粉（MS）或蔗糖（SU），此外包含20%蛋白质、16%混合脂肪，以及其他必需营养素与膳食纤维。结果显示，肥胖型大鼠的最终体质量为同窝瘦型大鼠的2~3倍，且两种表型大鼠在饲喂蔗糖日粮时的体质量均高于玉米淀粉日粮组。
2. 肩胛间棕色脂肪组织（interscapular brown adipose tissue，IBAT）质量在肥胖型大鼠中高于瘦型大鼠；在瘦型大鼠中，饲喂蔗糖日粮的IBAT质量高于玉米淀粉日粮组，但该差异在肥胖型大鼠中未显现。两种表型大鼠的IBAT细胞直径与脂肪细胞体积总体相近，且日粮碳水化合物类型对其无显著影响。
3. 两种表型大鼠的棕色脂肪细胞脂小室分布特征在定性上相似，且二者的形态学特征均提示存在产热活性。但肥胖型动物的脂小室分布中，产热活性较低的IV、V型棕色脂肪细胞占比高于同日粮处理的瘦型动物，而日粮类型对脂小室分布特征无影响。
4. 两种表型大鼠的血清三碘甲状腺原氨酸（T3）浓度相近；在瘦型大鼠中，饲喂蔗糖日粮的血清T3浓度高于玉米淀粉日粮组，但该效应在肥胖型大鼠中未出现。与之相反，血清甲状腺素（T4）浓度及甲状腺素摄取百分比不受日粮类型或大鼠表型的影响。
5. 本研究结果提示，肥胖型大鼠的棕色脂肪组织（BAT）介导的产热活性存在部分损伤，且该品系大鼠的肥胖可能并非由棕色脂肪组织产热功能的生化缺陷所致。