Hollander D, Dadufalza V
Division of Gastroenterology, University of California, Irvine 92717.
Exp Gerontol. 1990;25(1):61-5. doi: 10.1016/0531-5565(90)90010-y.
Vitamin A is a lipid soluble essential dietary micronutrient. Because aging individuals have elevated serum levels of vitamin A, we tested the intestinal absorptive capacity of the vitamin in aging rats by measuring the appearance rate of vitamin A in the lymphatic circulation as a measure of intestinal absorption. We infused the vitamin in a physiological concentration of 350 nM into the proximal jejunum of groups of Sprague-Dawley rats 2 to 23 months of age. Lymph was collected for 6 h and vitamin A radioactivity was measured. Lymph flow rate over 24 h ranged from 16 +/- 3.1 ml in the oldest to 21.5 +/- 2.4 ml in the youngest animals. Vitamin A transport into lymph was highest at 23 months of age, reaching 7869 +/- 154 pmol/6 h as compared to 6732 +/- 106 pmol/h at 2 months (p less than .01). The increase in vitamin A absorption with aging represented an increase from 35.6% of the infused vitamin at 2 months to 41.6% at 23 months of age. Because of the cumulative storage of vitamin A in the liver this increase in absorption and lymphatic appearance is of nutritional and metabolic significance. Increased lymphatic appearance of the vitamin could explain its higher absorption and serum levels in aging individuals.
维生素A是一种脂溶性必需膳食微量营养素。由于老年人血清维生素A水平升高，我们通过测量维生素A在淋巴循环中的出现率来衡量肠道吸收情况，以此测试老年大鼠对该维生素的肠道吸收能力。我们将生理浓度为350 nM的维生素注入2至23月龄的斯普拉格-道利大鼠组的空肠近端。收集淋巴液6小时并测量维生素A放射性。24小时内淋巴液流速范围从最年长动物的16±3.1毫升到最年幼动物的21.5±2.4毫升。维生素A转运至淋巴的量在23月龄时最高，达到7869±154皮摩尔/6小时，而2月龄时为6732±106皮摩尔/小时（p<0.01）。随着年龄增长，维生素A吸收增加，从2月龄时注入维生素的35.6%增至23月龄时的41.6%。由于维生素A在肝脏中的累积储存，这种吸收和淋巴出现率的增加具有营养和代谢意义。维生素在淋巴中的出现率增加可以解释其在老年人中较高的吸收率和血清水平。
