Downs Colleen T, McDonald Paula M, Brown Kelly, Ward David
School of Botany and Zoology, University of Natal, Private Bag X01, Scottsville, Pietermaritzburg, 3209, South Africa.
J Chem Ecol. 2003 Apr;29(4):845-58. doi: 10.1023/a:1022975531372.
The aim of this study was to investigate the dietary and physiological effects of condensed tannin ingestion on foregut fermenters, using Thallomys nigricauda, a folivorous rodent, as a model. We initially investigated the variability in physiological parameters, such as daily body mass (DMb), daily feed intake, daily fecal energy loss (FE), daily energy intake (DEI), daily urine pH, and daily urinary ammonia and urea concentrations, in response to different diets with low condensed tannin levels. This experiment was conducted to identify which physiological variables showed the least variation in the absence of tannin. In a second experiment, we investigated the response of the same dietary and physiological parameters to the effects of high dietary condensed tannin ingestion in T. nigricauda. We hypothesized that DMb, daily feed intake, FE, and DEI of T. nigricauda would be adversely affected by high dietary tannin content. We predicted that detoxification activity by T. nigricauda would increase at higher tannin levels. Ingestion of tannins affected the nutritional status of T. nigricauda, as shown by a decrease in body mass at high tannin levels. We also found that fewer ammonium ions were excreted in the urine by T. nigricauda, as would be expected if this were a means of regulating metabolic acidosis. The urine produced was more alkaline. This result indicates that T. nigricauda is not metabolizing these allelochemicals. Urea production was initially reduced, indicating conservation of bicarbonate ions that will neutralize blood acidity if there is detoxification. A diet choice experiment showed that tree rats avoid high tannin diets, even to the extent that they lose body mass on an alternative diet. This last-mentioned result is noteworthy because previous studies of the effects of tannins on herbivorous mammals have shown that there is physiological control rather than behavioral avoidance of the negative effects of tannin ingestion.
本研究的目的是，以食叶啮齿动物黑尾囊鼠为模型，调查摄入缩合单宁对前肠发酵动物的饮食和生理影响。我们首先研究了生理参数的变异性，如每日体重（DMb）、每日采食量、每日粪便能量损失（FE）、每日能量摄入量（DEI）、每日尿液pH值以及每日尿氨和尿素浓度，以应对不同低缩合单宁水平的饮食。进行该实验是为了确定在没有单宁的情况下，哪些生理变量的变化最小。在第二个实验中，我们研究了相同的饮食和生理参数对黑尾囊鼠摄入高膳食缩合单宁影响的反应。我们假设，高膳食单宁含量会对黑尾囊鼠的DMb、每日采食量、FE和DEI产生不利影响。我们预测，黑尾囊鼠的解毒活性会在较高单宁水平时增加。摄入单宁会影响黑尾囊鼠的营养状况，如在高单宁水平下体重下降所示。我们还发现，黑尾囊鼠尿液中排出的铵离子较少，这正如预期的那样，如果这是调节代谢性酸中毒的一种方式。产生的尿液碱性更强。这一结果表明，黑尾囊鼠没有代谢这些化感物质。尿素生成最初减少，表明如果存在解毒作用，会保留用于中和血液酸度所需的碳酸氢根离子。一项饮食选择实验表明，树鼠会避开高单宁饮食，甚至在选择其他饮食时体重会下降。最后提到的这个结果值得注意，因为之前关于单宁对草食性哺乳动物影响的研究表明，存在生理控制而非行为回避单宁摄入的负面影响。
