Rümenapf G, Schwille P O
Department of Surgery, University of Erlangen, FRG.
Calcif Tissue Int. 1988 May;42(5):326-30. doi: 10.1007/BF02556368.
Using in situ perfusion in the rat, we studied the duodenal bidirectional fluxes (LP, lumen-to-plasma; PL, plasma-to-lumen) and the net absorption of calcium (Ca) at progressive molar citrate:Ca ratios (1:1, 2.1:1, 8.5:1) and three pH levels (pH 5.0, 6.25, 7.0) of the Ca-containing (4 mmol/liter) perfusion solution. Rats perfused with pH-adjusted, citrate-free solutions served as controls. LP-flux and net calcium absorption (net CaA) fell dose-dependently with increasing citrate concentrations. Also, at a given citrate:Ca ratio, LP-flux and net CaA fell with increasing pH of the perfusion solution. PL-fluxes did not change from control values, irrespective of the composition of the perfusion solution. The concomitant serum Ca and parathyroid hormone levels as well as blood pH and bicarbonate, were largely unchanged under any of the citrate-containing perfusion solutions. In conclusion, citrate inhibits duodenal CaA of the rat pH- and dose-dependently, without changing intestinal Ca secretion. This effect is not related to changes in the acid-base status or to suppressed parathyroid gland function of the animals and may be best explained by dose- and pH-dependent intraluminal complex formation between Ca and citrate.
我们采用大鼠原位灌注法，研究了在含钙（4 mmol/升）灌注溶液中，当柠檬酸与钙的摩尔比逐渐变化（1:1、2.1:1、8.5:1）且pH值处于三个水平（pH 5.0、6.25、7.0）时，十二指肠的双向通量（LP，肠腔到血浆；PL，血浆到肠腔）以及钙的净吸收情况。用pH值调整且不含柠檬酸的溶液进行灌注的大鼠作为对照。随着柠檬酸浓度的增加，LP通量和钙净吸收量呈剂量依赖性下降。此外，在给定的柠檬酸与钙的比例下，LP通量和钙净吸收量随着灌注溶液pH值的升高而下降。无论灌注溶液的成分如何，PL通量与对照值相比均无变化。在任何含柠檬酸的灌注溶液条件下，大鼠的血清钙和甲状旁腺激素水平以及血液pH值和碳酸氢盐水平基本保持不变。总之，柠檬酸对大鼠十二指肠的钙吸收具有pH值和剂量依赖性抑制作用，而不改变肠道钙分泌。这种作用与动物酸碱状态的变化或甲状旁腺功能的抑制无关，可能最好的解释是钙与柠檬酸在肠腔内形成了剂量和pH值依赖性的复合物。
