Nonnecke B J, Horst R L, Hammell D C, Franklin S T
National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, 2300 Dayton Avenue, Ames, IA 50010, USA.
Int J Vitam Nutr Res. 2000 Dec;70(6):278-86. doi: 10.1024/0300-9831.70.6.278.
Neonatal calves are fed frequently milk replacers with vitamin A concentrations exceeding those recommended by the National Research Council. The vitamin A metabolite, retinoic acid (RA), affects profoundly cellular differentiation and homeostasis. For this reason, effects of dietary vitamin A on plasma concentrations of RA isomers in milk replacer-fed calves were examined. Male, Holstein calves (n = 24) were fed colostrum within 12 hours after birth and, thereafter, a custom-formulated low vitamin A milk replacer providing 0, 1700 [National Research Council (NRC) daily requirement for young growing calves] (controls), 34,000 (industry standard in the United States) or 68,000 IU of vitamin A daily. Concentrations of retinol and RA isomers in plasma samples collected from birth to 27 days of age were determined by HPLC. Retinol was affected by dietary vitamin A with higher concentrations occurring in calves supplemented with > or = 34,000 IU of vitamin A/day than in control (1700 IU of vitamin daily) and unsupplemented calves. Relative to controls, concentrations of all isomers of RA were higher in calves supplemented with > or = 34,000 of vitamin A daily during the experimental period. The predominant isomer in all calves was 9,13-dicis-RA. In control calves, 9,13-dicis-RA and 9-cis-RA were maximal at 1 to 6 days of age and then decreased progressively. In calves fed > or = 34,000 IU of vitamin A daily, concentrations of these isomers were markedly higher at 6 days of age, relative to controls, and remained elevated for the duration of the study. In all calves, retinol was correlated positively with 9,13-dicis- and 9-cis-RA from 9 to 27 days of age. 9,13-cis-Retinoic acid was correlated positively with 9-cis- and 13-cis-RA from 13 to 27 days of age. It is concluded that supplementing milk replacer-fed calves with vitamin A at levels exceeding current NRC recommendations by > or = 20-fold causes an elevation in plasma concentrations of retinol and retinoic acids. 9,13-dicis- and 9-cis-Retinoic acids were most affected by supplemental vitamin A. Physiologic consequences of increased plasma RA concentrations induced by high dietary levels of vitamin A warrant investigation.
新生犊牛经常被喂食维生素A浓度超过美国国家研究委员会推荐量的代乳品。维生素A的代谢产物视黄酸（RA）对细胞分化和体内平衡有深远影响。因此，研究了代乳品喂养的犊牛日粮中维生素A对血浆中RA异构体浓度的影响。雄性荷斯坦犊牛（n = 24）在出生后12小时内喂食初乳，此后，喂食定制的低维生素A代乳品，每日提供0、1700 [美国国家研究委员会（NRC）对生长中的幼犊的每日需求量]（对照组）、34000（美国行业标准）或68000国际单位的维生素A。通过高效液相色谱法测定从出生到27日龄采集的血浆样本中视黄醇和RA异构体的浓度。视黄醇受日粮维生素A的影响，补充维生素A≥34000国际单位/天的犊牛视黄醇浓度高于对照组（每日1700国际单位）和未补充维生素A的犊牛。相对于对照组，在实验期间，每日补充维生素A≥34000的犊牛所有RA异构体的浓度更高。所有犊牛中主要的异构体是9,13 - 二顺式 - RA。在对照犊牛中，9,13 - 二顺式 - RA和9 - 顺式 - RA在1至6日龄时达到最高，然后逐渐下降。在每日喂食维生素A≥34000国际单位的犊牛中，相对于对照组，这些异构体在日龄6天时浓度明显更高，并且在研究期间一直保持升高。在所有犊牛中，9至27日龄时视黄醇与9,13 - 二顺式 - RA和9 - 顺式 - RA呈正相关。13至27日龄时，9,13 - 顺式 - 视黄酸与9 - 顺式 - RA和13 - 顺式 - RA呈正相关。得出的结论是，给代乳品喂养的犊牛补充维生素A，使其水平超过当前NRC推荐量≥20倍，会导致血浆视黄醇和视黄酸浓度升高。9,13 - 二顺式 - RA和9 - 顺式 - RA受补充维生素A的影响最大。高日粮水平维生素A诱导的血浆RA浓度升高的生理后果值得研究。
