IN VITRO STUDIES OF INTESTINAL FLUORIDE ABSORPTION

氟(F)很容易穿过细胞膜和细胞层(例如， 胃肠道上皮)，这种转移被认为是 通过被动扩散发生。F转移的pH依赖性导致了 可渗透物种是未解离的氢氟酸的提议，以及那个细胞 膜对氟离子F-基本上是不透的。这已经是 在细菌和细胞悬浮液中表现出来。F转移的增加 对pH降低的反应也表现在肾脏排泄和 在胃和膀胱中的氟吸收。氟的吸收 尽管pH值很高，但很容易在小肠中发生，因此 极低的HF浓度和肠道F的pH依赖性 吸收还没有经过严格的分析。 这项建议针对的是这样一个问题：F是否会跨 小肠与游离HF浓度成正比？ 狗的小肠壁的节段将安装为平坦的 在双室孵化装置中的薄片和F从 不同条件下测得的粘膜至浆膜侧厚度 E浓度和pH。这是体外系统将被使用，因为它 避免复杂的整体动物吸收研究和许可 精确控制pH和总F、未解离的HF和氟离子F- 浓度。在任何情况下都可以计算出HF浓度 Henderson-Hasselbalch的pH和总氟浓度条件 方程式。通过系统地改变pH值和总氟浓度， 未解离的氢氟酸的浓度可以在很大范围内保持恒定 总氟浓度。此外，HF和F-浓度可以是 被操纵，使得它们都一起增加或减少，或者一个可能 增加，而另一个减少。通过操纵F浓度 和黏膜侧的pH值，并测量氟在粘膜上的积聚速度 浆膜侧氟转移与血药浓度的关系 可以研究不同的F种。

Fluoride (F) readily traverses cell membranes and cell layers (e.g., epithelia of the gastrointestinal tract), and this transfer is considered to occur by passive diffusion. The pH dependence of F transfer has led to the proposal that the permeable species is undissociated HF, and that cell membranes are essentially impermeable to fluoride ion F-. This has been demonstrated in bacteria and cell suspensions. An increase in F transfer in response to a lowering of pH has also been shown in renal excretion and in F absorption in the stomach and the urinary bladder. Absorption of F occurs very readily in the small intestine despite the high pH and hence extremely low HF concentration, and the pH dependence of intestinal F absorption has not been subjected to rigorous analysis. This proposal is directed toward the question: Is F transfer across the small intestine directly proportional to undissociated HF concentration? Segments of wall of the small intestine of dogs will be mounted as flat sheets in a two-chamber incubation apparatus, and the transfer of F from the mucosal to the serosal side measured under varying conditions of total E concentration and pH. This is vitro system will be used because it avoids the complexities of whole animal absorption studies and permits precise control of pH and of total F, undissociated HF and fluoride ion F- concentrations. The HF concentration can be calculated under any conditions of pH and total F concentration from the Henderson-Hasselbalch equation. By systematically varying pH and total F concentration, the concentration of undissociated HF can be held constant over a wide range of total F concentration. In addition, the HF and F- concentrations can be manipulated so that they both increase or decrease together, or one may increase while the other decreases. By manipulating the F concentrations and pH on the mucosal side and measuring the rate of F accumulation on the serosal side, the relationship between F transfer and concentrations of the different F species can be investigated.