Miles J M, Ellman M G, McClean K L, Jensen M D
Am J Physiol. 1987 Mar;252(3 Pt 1):E431-8. doi: 10.1152/ajpendo.1987.252.3.E431.
The accuracy of tracer methods for estimating free fatty acid (FFA) rate of appearance (Ra), either under steady-state conditions or under non-steady-state conditions, has not been previously investigated. In the present study, endogenous lipolysis (traced with 14C palmitate) was suppressed in six mongrel dogs with a high-carbohydrate meal 10 h before the experiment, together with infusions of glucose, propranolol, and nicotinic acid during the experimental period. Both steady-state and non-steady-state equations were used to determine oleate Ra ([3H]oleate) before, during, and after a stepwise infusion of an oleic acid emulsion. Palmitate Ra did not change during the experiment. Steady-state equations gave the best estimates of oleate inflow approximately 93% of the known oleate infusion rate overall, while errors in tracer estimates of inflow were obtained when non-steady-state equations were used. The metabolic clearance rate of oleate was inversely related to plasma concentration (P less than 0.01). In conclusion, accurate estimates of FFA inflow were obtained when steady-state equations were used, even under conditions of abrupt and recent changes in Ra. Non-steady-state equations, in contrast, may provide erroneous estimates of inflow. The decrease in metabolic clearance rate during exogenous infusion of oleate suggests that FFA transport may follow second-order kinetics.
在稳态或非稳态条件下，用于估计游离脂肪酸（FFA）生成率（Ra）的示踪剂方法的准确性此前尚未得到研究。在本研究中，在实验前10小时用高碳水化合物餐抑制了6只杂种犬的内源性脂肪分解（用14C棕榈酸示踪），并在实验期间输注葡萄糖、普萘洛尔和烟酸。在逐步输注油酸乳剂之前、期间和之后，使用稳态和非稳态方程来测定油酸Ra（[3H]油酸）。实验期间棕榈酸Ra没有变化。稳态方程对油酸流入的估计最为准确，总体上约为已知油酸输注率的93%，而使用非稳态方程时，示踪剂对流入的估计存在误差。油酸的代谢清除率与血浆浓度呈负相关（P<0.01）。总之，即使在Ra突然且近期发生变化的情况下，使用稳态方程也能获得FFA流入的准确估计。相比之下，非稳态方程可能会提供错误的流入估计。外源性输注油酸期间代谢清除率的降低表明FFA转运可能遵循二级动力学。
