van Vliet T, van Vlissingen M F, van Schaik F, van den Berg H
Department of Physiology and Kinetics, TNO Nutrition and Food Research Institute, Zeist, Netherlands.
J Nutr. 1996 Feb;126(2):499-508. doi: 10.1093/jn/126.2.499.
The purpose of this study was to examine whether intestinal beta-carotene cleavage activity, measured with the dioxygenase assay, is affected by vitamin A intake and whether this in vitro activity is a determinant of beta-carotene cleavage in vivo, measured in lymph-cannulated rats. Six groups of 10-20 rats were fed a diet with a low, normal or high retinyl palmitate concentration (120 RE, 1200 RE and 12,000 RE per kg, respectively) for 14 to 18 wk, either supplemented or not with 50 mg beta-carotene/kg in the last 6 wk. Intestinal dioxygenase activity was 90% higher (P < 0.05) in the animals fed the unsupplemented low vitamin A diet than in the animals fed the unsupplemented high vitamin A diet, whereas in beta-carotene-supplemented rats intestinal dioxygenase activity was significantly lower than in unsupplemented rats. The molar ratio between retinyl esters and beta-carotene in lymph collected over 8 h after a single intestinal dose of beta-carotene (250 micrograms) to beta-carotene-unsupplemented rats fed the three levels of vitamin A was correlated with intestinal dioxygenase activity (r = 0.66, P = 0.003). Dioxygenase activity in the liver was not affected by the vitamin A concentration of the diet but was 70% higher in the beta-carotene-supplemented rats. Based on the difference in liver vitamin A contents between beta-carotene-supplemented and unsupplemented rats we estimated beta-carotene conversion factors of 9:1 for the rats fed the high vitamin A diet and 4:1 for the rats fed the normal and low vitamin A diets. Intestinal beta-carotene cleavage activity is higher in vitamin A-deficient rats than in rats with a high intake of either vitamin A or beta-carotene. The intestinal dioxygenase activity as measured in vitro is an adequate indicator of in vivo beta-carotene cleavage activity.
本研究的目的是检测用双加氧酶分析法测定的肠道β-胡萝卜素裂解活性是否受维生素A摄入量的影响，以及这种体外活性是否是在淋巴插管大鼠体内测定的β-胡萝卜素裂解的一个决定因素。将六组10 - 20只大鼠分别喂食含低、正常或高浓度棕榈酸视黄酯的饲料（分别为每千克120 RE、1200 RE和12,000 RE），持续14至18周，在最后6周时，部分组添加或不添加50 mg/kg的β-胡萝卜素。与喂食未添加高维生素A饲料的动物相比，喂食未添加低维生素A饲料的动物肠道双加氧酶活性高90%（P < 0.05），而在添加β-胡萝卜素的大鼠中，肠道双加氧酶活性显著低于未添加的大鼠。给喂食三种维生素A水平的未添加β-胡萝卜素的大鼠单次经肠道给予β-胡萝卜素（250微克）后，在8小时内收集的淋巴中视黄酯与β-胡萝卜素的摩尔比与肠道双加氧酶活性相关（r = 0.66，P = 0.003）。肝脏中的双加氧酶活性不受饲料中维生素A浓度的影响，但在添加β-胡萝卜素的大鼠中高70%。根据添加β-胡萝卜素和未添加β-胡萝卜素的大鼠肝脏维生素A含量的差异，我们估计喂食高维生素A饲料的大鼠β-胡萝卜素转化系数为9:1，喂食正常和低维生素A饲料的大鼠为4:1。维生素A缺乏的大鼠肠道β-胡萝卜素裂解活性高于高摄入维生素A或β-胡萝卜素的大鼠。体外测定的肠道双加氧酶活性是体内β-胡萝卜素裂解活性的一个充分指标。
