Krieger N S, Stathopoulos V M, Bushinsky D A
Department of Medicine, University of Rochester School of Medicine, New York 14642, USA.
Am J Physiol. 1996 Jul;271(1 Pt 1):C130-5. doi: 10.1152/ajpcell.1996.271.1.C130.
As a model of human hypercalciuria, we have selectively inbred genetic hypercalciuric stone-forming (GHS) Sprague-Dawley rats whose mean urine calcium excretion is eight to nine times greater than that of controls. A large component of this excess urine calcium excretion is secondary to increased intestinal calcium absorption, which is not due to an elevation in serum 1,25(OH)2D3, but appears to result from an increased number of intestinal 1,25(OH)2D3 receptors (VDR). When GHS rats are fed a low-calcium diet, the hypercalciuria is only partially decreased and urine calcium excretion exceeds intake, suggesting that an additional mechanism contributing to the hypercalciuria is enhanced bone demineralization. To determine if GHS rat bones are more sensitive to exogenous 1,25(OH)2D3, we cultured calvariae from neonatal (2- to 3-day-old) GHS and control rats with or without 1,25(OH)2D3 or parathyroid hormone (PTH) for 48 h at 37 degrees C. There was significant stimulation of calcium efflux from GHS calvariae at 1 and 10 nM 1,25(OH)2D3, whereas control calvariae showed no significant response to 1,25(OH)2D3 at any concentration tested. In contrast, PTH induced similar bone resorption in control and GHS calvariae. Immunoblot analysis demonstrated a fourfold increase in the level of VDR in GHS calvariae compared with control calvariae, similar to the increased intestinal receptors described previously. There was no comparable change in VDR RNA levels as measured by slot blot analysis, suggesting the altered regulation of the VDR occurs posttranscriptionally. That both bone and intestine display an increased amount of VDR suggests that this may be a systemic disorder in the GHS rat and that enhanced bone resorption may be responsible, in part, for the hypercalciuria in the GHS rat.
作为人类高钙尿症的模型，我们选择性地培育了遗传性高钙尿结石形成（GHS）的近交系Sprague-Dawley大鼠，其平均尿钙排泄量比对照组高八到九倍。这种过量尿钙排泄的很大一部分继发于肠道钙吸收增加，这并非由于血清1,25(OH)2D3升高，而是似乎源于肠道1,25(OH)2D3受体（VDR）数量增加。当给GHS大鼠喂食低钙饮食时，高钙尿症仅部分减轻，且尿钙排泄超过摄入量，这表明导致高钙尿症的另一种机制是骨脱矿增强。为了确定GHS大鼠骨骼对外源性1,25(OH)2D3是否更敏感，我们在37℃下将新生（2至3日龄）GHS大鼠和对照大鼠的颅骨在有或无1,25(OH)2D3或甲状旁腺激素（PTH）的情况下培养48小时。在1和10 nM 1,25(OH)2D3时，GHS颅骨的钙流出有显著刺激，而对照颅骨在任何测试浓度下对1,25(OH)2D3均无显著反应。相比之下，PTH在对照和GHS颅骨中诱导了相似的骨吸收。免疫印迹分析表明，与对照颅骨相比，GHS颅骨中VDR水平增加了四倍，这与先前描述的肠道受体增加相似。通过狭缝印迹分析测量，VDR RNA水平没有可比变化，这表明VDR的调节改变发生在转录后。骨骼和肠道中VDR数量均增加表明，这可能是GHS大鼠的一种全身性疾病，骨吸收增强可能部分导致了GHS大鼠的高钙尿症。
