Parathyroid sensing of the direction of change of calcium in uremia.

It could be advantageous for the parathyroids to be able to sense not only the absolute concentration of extracellular Ca2+, but also the rate and direction of change of Ca2+, thereby allowing the parathyroids to respond earlier to threats to Ca2+ homeostasis. By using high and low Ca2+ dialysis in a single session, we examined the parathyroid response to direction of change of Ca2+ during acute Ca2+ perturbation in nine hemodialysis patients. Separate PTH/ionized calcium (PTH/iCa) response curves were generated for rising Ca2+ and falling Ca2+. Significant directional hysteresis (higher PTH level during falling than during rising Ca2+) was found. During hypercalcemia, PTH levels were between 2.2 and 1.6 times higher at iCa concentrations of between 0 and +0.1 mM above the baseline iCa, when Ca2+ was falling than when it was rising. During the phase of induced hypocalcemia, parathyroid fatigue was seen in six of the nine patients. Fatigue patients tended to have higher basal PTH (1-84) levels than those not showing fatigue. The existence of fatigue provides an explanation for directional hysteresis during hypocalcemia, and therefore parathyroid sensing of the direction of change of Ca2+ could not be assessed during hypocalcemia. These studies demonstrate a capacity of the parathyroids to sense the direction of movement of Ca2+ during hypercalcemia.

甲状旁腺不仅能够感知细胞外Ca2 +的绝对浓度，还能感知Ca2 +变化的速率和方向，这可能是有利的，从而使甲状旁腺能够更早地对Ca2 +内稳态受到的威胁作出反应。通过在单次透析过程中使用高钙和低钙透析，我们研究了9名血液透析患者在急性Ca2 +波动期间甲状旁腺对Ca2 +变化方向的反应。分别针对Ca2 +升高和降低生成了甲状旁腺激素/离子化钙（PTH/iCa）反应曲线。发现了明显的方向滞后性（Ca2 +下降时的PTH水平高于上升时）。在高钙血症期间，当Ca2 +下降时，在离子化钙浓度比基线离子化钙高0到 +0.1 mM之间时，PTH水平比Ca2 +上升时高2.2到1.6倍。在诱发的低钙血症阶段，9名患者中有6名出现甲状旁腺疲劳。出现疲劳的患者往往比未出现疲劳的患者具有更高的基础PTH（1 - 84）水平。疲劳的存在为低钙血症期间的方向滞后性提供了一种解释，因此在低钙血症期间无法评估甲状旁腺对Ca2 +变化方向的感知。这些研究表明甲状旁腺在高钙血症期间具有感知Ca2 +移动方向的能力。