芳香族和脂环族化合物在反刍家畜消化道中的释放代谢机制

Metabolism of aromatic and alicylic compounds in the digestive tract of ruminants

芳香族和脂环族化合物(异生物素)在反刍动物体内的消化代谢水平主要取决于瘤胃的消化代谢能力,而这种能力是由瘤胃微生物决定的;瘤胃微生物在厌氧环境下具有降解芳香族异生物素的潜力,咀嚼有助于植物细胞壁脂化酚酸及其内容物的酚化合物的释放,释放后的代谢物大部分在瘤胃内被微生物代谢;瘤胃微生物糖酶的作用,使与细胞壁结合的酚酸以可溶性酯—糖单元的形式从牧草中释放出来,在肠道内微生物水解活动可引起植物中自然存在的结合态酚酸释放成游离态;细胞壁酯化的p-香豆酸含量与体内细胞壁消化率、体外干物质消化率和半体内瘤胃纤维降解率呈显著负相关,草本植物的木质素含量与细胞壁降解率也常为负相关;异生物素对动物和微生物具有毒害作用,但在瘤胃的厌氧微生物作用下,通过水解、还原、取代和脱羧等反应,异生物素发生生物转化和矿化,其还原代谢产物的毒性远低于其前体物。芳香族化合物在反刍家畜消化道中的释放代谢机制的研究,为其代谢物在尿液中的排泄含量作为反刍动物采食量的预测指标的可行性和机理从代谢水平上奠定基础。

The level of metabolizing aromatic and alicylic compounds in ruminant body depends on the (metabolizing) capacity of rumen where microorganisms play an important role. Under anaerobic condition in rumen, microbial metablism is the main pathway by which xenobiotics were degraded. Aromatic xenobiotics released after mastication have three fates in the digestive tract-absorbed, bounded to unavailable proteins and (lipids) of the digesta (leading) to excretion in the faeces, and mostly metabolized in rumen by microbial activities and reactions such as hydrolysis, reduction, decarboxylation, O-dealkylation, dehydroxylation and (hydrogenation). Besides, cell wall (CW) bound phenolic acids can also be released from forages as soluble esters with carbohydrates due to the action of carbohydrases from rumen microorganisms. Subsequently, the (xenobiotics) are partial degraded (biotransformation) and complete degraded (mineralisation) and, as a result, the toxicity become far less from their precursors. It has also found that the content of CW-esterified (p-coumaric) acid has significant negative correlations with CW digestibility in vivo, dry matter digestibility (DMD) in vitro and ruminal cellulose degradability (so does as the lignin content) in sacco. The review and summary of rumen metabolisation of aromatic xenobiotics provide a base for predicting feed intake of grazing ruminants according with their contents in urine.