Odle J
Department of Animal Science, North Carolina State University, Raleigh 27695, USA.
J Nutr. 1997 Jun;127(6):1061-7. doi: 10.1093/jn/127.6.1061.
Because of their unique digestive and metabolic properties, medium-chain triglycerides (MCT) are used in a variety of nutritional settings, including use as a readily digestible energy source for the neonate. This review examines recent findings from our laboratory related to MCT digestion and metabolism that are drawn from a neonatal piglet model, but which may be clinically relevant to human infants. We have shown that MCT utilization improves rapidly with postnatal age (within 24 h), which is likely due to the ontogeny of pancreatic lipase. Additional data delineate the dramatic effects of emulsification and fatty acid chain length (within the medium-chain family) on utilization, with the suggestion that triacylhexanoate is utilized at the highest rate. Again, these effects are likely mediated via an increase in the kinetics of digestion rather than metabolism. Indeed, using both in vitro and in vivo radiotracer techniques, we were unable to detect metabolic differences among even-chain fatty acid homologues. However, studies with isolated hepatocytes have shown greater oxidation rates of odd-chain fatty acids compared with even-chain homologues, in part as a result of the anaplerotic potential of propionyl-CoA arising from odd-carbon fatty acid oxidation. In vivo radiotracer studies also showed an improvement in octanoate oxidation to CO2, with a concomitant reduction in urinary dicarboxylic acid excretion when colostrum-deprived piglets were supplemented with L-carnitine. Further metabolic research led to the novel finding that piglets have a very limited hepatic capacity to synthesize ketone bodies, and that acetate may be a relatively important product of hepatic fatty acid oxidation in this species.
由于中链甘油三酯（MCT）具有独特的消化和代谢特性，它们被用于多种营养环境中，包括作为新生儿易于消化的能量来源。本综述探讨了我们实验室最近从新生仔猪模型中获得的与MCT消化和代谢相关的研究结果，这些结果可能与人类婴儿的临床情况相关。我们已经表明，MCT的利用率随着出生后的年龄（24小时内）迅速提高，这可能是由于胰腺脂肪酶的个体发育。其他数据描述了乳化和脂肪酸链长度（在中链家族内）对利用率的显著影响，表明己酸甘油三酯的利用率最高。同样，这些影响可能是通过消化动力学的增加而不是代谢来介导的。事实上，使用体外和体内放射性示踪技术，我们无法检测到偶数链脂肪酸同系物之间的代谢差异。然而，对分离的肝细胞的研究表明，奇数链脂肪酸的氧化速率比偶数链同系物更高，部分原因是奇数碳脂肪酸氧化产生的丙酰辅酶A的回补潜力。体内放射性示踪研究还表明，给初乳缺乏的仔猪补充L-肉碱后，辛酸氧化为二氧化碳的能力有所提高，同时尿中二羧酸的排泄减少。进一步的代谢研究导致了一个新的发现，即仔猪肝脏合成酮体的能力非常有限，并且乙酸盐可能是该物种肝脏脂肪酸氧化的一个相对重要的产物。
