Keagy E M, Carew L B, Alster F A, Tyzbir R S
Department of Animal Sciences, University of Vermont, Burlington 05405.
J Nutr. 1987 Sep;117(9):1532-40. doi: 10.1093/jn/117.9.1532.
Protein-deficient diets (17, 10, 6.5 or 3% protein) and a 24% control diet were fed to growing chicks. A control group was pair-fed daily with each deficient group. Energy intake was lower in the 6.5 and 3% protein groups than in the other groups. However, weight gain, bone growth and feed conversion efficiency were lower with 10% protein or less. Relative thyroid weights were unaffected by dietary protein. Plasma T3 (3,5,3'-triiodothyronine) levels were significantly higher in all deficient groups, whereas plasma T4 (thyroxine) was lower. Plasma rT3 (reverse T3) was unaffected by the protein deficiencies, suggesting that enhanced conversion of T4 to T3 rather than to rT3 had occurred. Hepatic alpha-glycerol-3-phosphate dehydrogenase (alpha-GP) shuttle activity increased markedly in protein-deficient chicks. Efficiency of energy utilization was unaltered in chicks fed 17 or 10% protein but was higher in chicks fed 6.5 and 3% protein than in controls. All deficient chicks had more fat and less protein and water in the tissues. The lower feed conversion efficiency therefore represents almost entirely a shift in body composition toward fat and does not reflect a loss of energy as heat. We conclude that elevations in plasma T3 and in thyroid-controlled alpha-GP shuttle activity, although sensitive indicators of protein deficiencies, are not good predictors of altered thermogenic activity in protein-deficient chicks.
将蛋白质含量分别为17%、10%、6.5%或3%的缺乏蛋白质饮食以及24%的对照饮食投喂给生长中的雏鸡。对照组每天与每个缺乏蛋白质的组进行配对投喂。蛋白质含量为6.5%和3%的组的能量摄入量低于其他组。然而，蛋白质含量为10%或更低时，体重增加、骨骼生长和饲料转化效率较低。相对甲状腺重量不受日粮蛋白质的影响。所有缺乏蛋白质的组的血浆三碘甲状腺原氨酸（T3）水平显著更高，而血浆甲状腺素（T4）水平较低。血浆反三碘甲状腺原氨酸（rT3）不受蛋白质缺乏的影响，这表明发生了T4向T3而非向rT3的转化增强。蛋白质缺乏的雏鸡肝脏中α-甘油-3-磷酸脱氢酶（α-GP）穿梭活性显著增加。投喂17%或10%蛋白质的雏鸡的能量利用效率未改变，但投喂6.5%和3%蛋白质的雏鸡的能量利用效率高于对照组。所有缺乏蛋白质的雏鸡组织中的脂肪更多，蛋白质和水分更少。因此，较低的饲料转化效率几乎完全代表了身体组成向脂肪的转变，而不是能量以热量形式的损失。我们得出结论，血浆T3升高和甲状腺控制的α-GP穿梭活性增加，虽然是蛋白质缺乏的敏感指标，但并不是蛋白质缺乏雏鸡产热活性改变的良好预测指标。
