Kelley S K, Green M H
Nutrition Department and Graduate Physiology Program, The Pennsylvania State University, University Park, PA 16802, USA.
J Nutr. 1998 Oct;128(10):1767-73. doi: 10.1093/jn/128.10.1767.
We studied relationships among vitamin A intake, liver levels of vitamin A, plasma retinol concentrations and the irreversible utilization of vitamin A. To supplement existing data, we first used model-based compartmental analysis to determine vitamin A utilization and other kinetic parameters in male Sprague-Dawley rats that had adequate liver vitamin A stores ( approximately 9000 nmol) and were fed a diet containing low levels of vitamin A. Plasma retinol kinetics were monitored for 43 d after administration of [3H]retinol-labeled plasma to rats consuming approximately 23 (Group 1, n = 6) or approximately 4.2 (Group 2, n = 6) nmol vitamin A/d. Data for plasma tracer vs. time and for tracer lost irreversibly by the end of the experiment, were fit to a three-compartment model in which plasma retinol exchanges with vitamin A in two kinetically distinct extravascular compartments. Irreversible utilization rates ( approximately 41 nmol/d) were similar to those for rats that are in vitamin A balance, suggesting that, when liver vitamin A stores are adequate, utilization rate is not decreased to compensate for a low vitamin A intake. Multiple linear regression analysis was then used to relate these and previously collected data (total, 62 rats) on vitamin A intake (4. 2-49 nmol/d), plasma retinol concentration (1.4-2.5 micromol/L) and liver vitamin A level (1.2-11,000 nmol) to vitamin A utilization (disposal rate, 4.2-68 nmol/d). A significant relationship (R2(adj) = 0.93) was found for the equation [disposal rate (nmol/d) = -0.720 (nmol/d) + 0.844 (d-1).(plasma retinol; nmol) + 0.00139 (d-1).(liver vitamin A; nmol) + 0.220.(vitamin A intake; nmol/d)]. Plasma retinol accounted for 92% of the variability in disposal rate (vs. 5% for liver vitamin A and 3% for vitamin A intake). We conclude that plasma retinol is a main determinant of the irreversible utilization of vitamin A in rats with low to moderate vitamin A intake.
我们研究了维生素A摄入量、肝脏维生素A水平、血浆视黄醇浓度与维生素A不可逆利用之间的关系。为补充现有数据，我们首先使用基于模型的房室分析来确定雄性Sprague-Dawley大鼠的维生素A利用情况及其他动力学参数，这些大鼠肝脏维生素A储备充足（约9000 nmol），且喂食低水平维生素A的日粮。给每日摄入约23（第1组，n = 6）或约4.2（第2组，n = 6）nmol维生素A的大鼠注射[3H]视黄醇标记的血浆后，监测其血浆视黄醇动力学43天。将血浆示踪剂随时间变化的数据以及实验结束时不可逆损失的示踪剂数据，拟合到一个三室模型中，其中血浆视黄醇与两个动力学上不同的血管外室中的维生素A进行交换。不可逆利用率（约41 nmol/d）与处于维生素A平衡状态的大鼠相似，这表明当肝脏维生素A储备充足时，利用率不会降低以补偿低维生素A摄入量。然后使用多元线性回归分析将这些数据以及之前收集的关于维生素A摄入量（4.2 - 49 nmol/d）、血浆视黄醇浓度（1.4 - 2.5 μmol/L）和肝脏维生素A水平（1.2 - 11,000 nmol）的数据（总共62只大鼠）与维生素A利用情况（处置率，4.2 - 68 nmol/d）相关联。对于方程[处置率（nmol/d）= -0.720（nmol/d）+ 0.844（d - 1）·（血浆视黄醇；nmol）+ 0.00139（d - 1）·（肝脏维生素A；nmol）+ 0.220·（维生素A摄入量；nmol/d）]，发现了显著关系（R2(adj) = 0.93）。血浆视黄醇占处置率变异性的92%（相比之下，肝脏维生素A占5%，维生素A摄入量占3%）。我们得出结论，对于维生素A摄入量低至中等的大鼠，血浆视黄醇是维生素A不可逆利用的主要决定因素。
