根田鼠对食物单宁酸的解毒代价

Metabolic costs (Microtus oeconomus) of tannic acid in root voles

在实验室条件下,测定了根田鼠对单宁酸的解毒代价。结果表明,在食物蛋白质为10%的条件下,摄食3%和6%单宁酸食物的根田鼠经尿液分泌的葡萄糖醛酸较对照组分别增加13.77%和38.80%;与对照组比较,在食物蛋白质为20%的条件下,摄食3%和6%单宁酸食物的实验个体尿液分泌的葡萄糖醛酸分别增加6.11%和22.25%。在食物蛋白质为10%时,用3%和6%单宁酸食物处理的个体,其尿液NH+4-N含量较对照组个体分别增加51.69%和198.44%。在食物中蛋白质为20%时,摄食3%和6%单宁酸食物的试验个体,其尿液中的NH+4-N含量分别较对照组高1.72%和74.19%。由此说明,单宁酸能显著增加根田鼠尿液葡萄糖醛酸分泌量,根田鼠尿液的NH+4-N的含量随食物单宁酸增加而增高,从而增加动物机体对单宁酸的代谢价。

Years of coevolution between plants and herbivores have resulted in a diverse array of plant defenses and herbivore counter\|defense. Tannins, a diverse group of polar, high molecular weight, found in many vascular plants (especially woody perennials), are characterized by their ability to precipitate proteins. Plant tannins affect many aspects of the consumer's digestion and metabolism, such as feed intake, dietary protein availability, activity of digestive enzyme, detoxification activity, postabsorptive metabolism and reproduction.Previous studies have focused on the metabolism of secondary compounds in the digestive tract. Rapid absorption may avoid potential interactions between secondary compounds and other components, but absorbed secondary compounds must be detoxified and excreted, and the cost of these processes is largely unknown. This study was therefore designed to investigate the metabolic cost of tannic acid in root vole (Microtus oeconomus). Experimental voles came from a root vole colony maintained at the Northwest Plateau Institute of Biology, Chinese Academy of Science, Xi'ning, Qinghai. Founders for the colony were caught at the Haibei Alpine Ecological System Station of Academia Sinica in May 1998. Experimental diets were prepared by adding tannic acid (Tannin Corporation, Peabody MA) at 3% and 6% of total dry matter of the diet. To study the protein  tannic acid interaction, 2 levels of dietary protein, i.e., 10% and 20%, were designed. As a result, 6 diets were prepared. The crude fiber, digestible energy and crude ash of diets were at the same level to minimize the effects of those nutrients. Thirty unpregnant female root voles were randomly divided into 6 groups and assigned to one of 6 diets for 3weeks. The results indicated that voles fed 3% and 6% tannic acid diets were 1377% and 3880% respectively higher in urinary glucuronic acid levels than controls at low level of protein. When given the high protein diet, voles fed 3 and 6% tannic acid were 61 and 223% respectively higher than controls. This pattern reflected that the excretion of urinary NH+4N when given the 10% protein diet, whereas those given 6% but not 3% tannic acid diet excreted significantly more urinary NH+4N when given the 20% protein diet. Thus elevated NH+4N excretion indicated an additional nitrogen cost to the voles, and the actual cost of detoxification of tannic acid was probably much higher than expected. This study suggested that increasing excretion of urinary glucuronic acid and NH+4N in voles given additional dietary tannic acid was a consequence of the cost of the detoxification process.