Wright C L, Spears J W, Webb K E
Department of Animal Science and Interdepartmental Nutrition Program, North Carolina State University, Raleigh 27695-7621, USA.
J Anim Sci. 2008 Jun;86(6):1357-63. doi: 10.2527/jas.2006-650. Epub 2008 Feb 29.
Uptake and transport of Zn from (65)Zn-labeled ZnSO(4) and Zn proteinate (ZnProt) by ruminal and omasal epithelia were examined by using a parabiotic chamber system. Uptake was measured during a 4-h incubation with 10, 20, or 200 microM Zn as ZnSO(4) or ZnProt in the mucosal buffer (pH 6.0, Krebs-Ringer phosphate). Zinc uptake and transport were also evaluated after simulated ruminal digestion. Buffered ruminal fluid contained a feed substrate and 10 or 200 microM added Zn as ZnSO(4) or ZnProt. In a preliminary experiment, uptake of Zn by omasal tissue was low; thus, the remaining experiments were conducted solely with ruminal epithelium. Incubations to determine the effect of time on Zn uptake from mucosal buffer containing 20 microM added Zn as ZnSO(4) or ZnProt resulted in increased (P < 0.01) Zn uptake as incubation time increased from 30 to 240 min. Zinc uptake was also greater (P = 0.02) from mucosal buffer containing ZnProt compared with ZnSO(4). Zinc uptake from incubations containing 10 or 200 microM was affected by source x concentration (P = 0.05) and concentration x time (P < 0.01) interactions. With 10 microM Zn, uptake was not influenced by Zn source, whereas when 200 microM Zn was added, Zn uptake from ZnProt was greater than from ZnSO(4). Increasing incubation time resulted in increased Zn uptake with 200 microM Zn in the mucosal buffer; however, with 10 microM Zn, uptake did not change after 30 min. After simulated ruminal fermentation, the proportion of Zn in a soluble form was influenced by a source x concentration interaction (P = 0.03). After 18 h of incubation, the proportion of Zn that was soluble was not different between ZnProt and ZnSO(4) in buffered ruminal fluid that contained 10 microM added Zn, but was greater for ZnProt compared with ZnSO(4) with 200 microM Zn in the incubation. Zinc uptake from the aqueous fractions of simulated ruminal digestions containing 200 microM added Zn was greater (P < 0.01) than from those containing 10 microM added Zn. Zinc transport, based on detection of (65)Zn in serosal buffer, did not occur in any of the experiments. The results of the current experiments suggest that absorption of Zn into the bloodstream does not occur from the ruminant foresto-mach; however, Zn uptake occurs in ruminal tissue and is greater from ZnProt than from ZnSO(4).
采用联体腔室系统研究了瘤胃和网胃上皮对（65）Zn标记的硫酸锌（ZnSO₄）和蛋白锌（ZnProt）中锌的摄取和转运。在黏膜缓冲液（pH 6.0，磷酸 Krebs-Ringer 液）中，用 10、20 或 200 μmol/L 的 ZnSO₄ 或 ZnProt 进行 4 小时孵育，测定摄取量。在模拟瘤胃消化后也评估了锌的摄取和转运。缓冲的瘤胃液含有一种饲料底物以及 10 或 200 μmol/L 添加的 ZnSO₄ 或 ZnProt。在一项初步实验中，网胃组织对锌的摄取较低；因此，其余实验仅用瘤胃上皮进行。为确定时间对从含 20 μmol/L 添加锌（以 ZnSO₄ 或 ZnProt 形式）的黏膜缓冲液中锌摄取的影响而进行的孵育实验中，随着孵育时间从 30 分钟增加到 240 分钟，锌摄取量增加（P < 0.01）。与 ZnSO₄ 相比，含 ZnProt 的黏膜缓冲液中的锌摄取量也更高（P = 0.02）。含 10 或 200 μmol/L 的孵育实验中，锌摄取受来源×浓度（P = 0.05）和浓度×时间（P < 0.01）相互作用的影响。对于 10 μmol/L 的锌，摄取不受锌来源影响，而当添加 200 μmol/L 的锌时，从 ZnProt 摄取的锌比从 ZnSO₄ 摄取的更多。在黏膜缓冲液中添加 200 μmol/L 的锌时，孵育时间增加导致锌摄取增加；然而，添加 10 μmol/L 的锌时，30 分钟后摄取量没有变化。模拟瘤胃发酵后，可溶形式锌的比例受来源×浓度相互作用的影响（P = 0.03）。孵育 18 小时后，在含 10 μmol/L 添加锌的缓冲瘤胃液中，ZnProt 和 ZnSO₄ 中可溶锌的比例没有差异，但在孵育液中添加 200 μmol/L 锌时，ZnProt 中可溶锌的比例比 ZnSO₄ 更高。从含 200 μmol/L 添加锌的模拟瘤胃消化液的水相中摄取的锌比含 10 μmol/L 添加锌的更高（P < 0.01）。基于在浆膜缓冲液中检测到（65）Zn，在任何实验中均未发生锌的转运。当前实验结果表明反刍动物前胃向血液中吸收锌的过程不会发生；然而，瘤胃组织中会发生锌的摄取，且从 ZnProt 摄取的量比从 ZnSO₄ 摄取的更多。
