Effect of vitamin D status on the equilibrium between occupied and unoccupied 1,25-dihydroxyvitamin D intestinal receptors in the chick.
Effect of vitamin D status on the equilibrium between occupied and unoccupied 1,25-dihydroxyvitamin D intestinal receptors in the chick.
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维生素 D 状态对小鸡中占用和未占用 1,25-二羟基维生素 D 肠道受体之间平衡的影响。
DOI：
10.1172/jci110522
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发表时间：
1982
期刊：
影响因子：
--
通讯作者：
Norman,AW
中科院分区：
文献类型：
--
作者：
Hunziker,W;Walters,MR;Bishop,JE;Norman,AW
通过先前报道的交换试验研究了鸡肠粘膜的体内占据和未占据的1，25-二羟基维生素D3[1，25（OH）2D 3]受体之间的动态平衡[（1980）. J. Biol. Chem. 255：9534-9537]。这些参数及其与生物反应的相关性，即，在不同的生理条件下评估肠维生素D依赖性钙结合蛋白（CaBP）的水平。在单次注射1，25（OH）2D 3（3.25 nmol）后，占据的受体水平在1和2 h之间急剧增加至最大值，随后迅速下降。1α-羟基维生素D3[1α（OH）D3]是一种需要25-羟基化才能发挥生物活性的类似物，单次给药导致了一种延长的反应，尽管反应较低，在注射后6 h达到最大受体占有率，24 h达到最大水平的一半。肠受体结合模式反映了1，25（OH）2D 3或1α（OH）D3治疗后血清1，25（OH）2D 3水平。此外，1，25（OH）2D 3和占据受体水平的血液消失的时间过程（半衰期）相似（分别为1.9和2.3 h），表明占据的1，25（OH）2D 3受体的量由血清1，25（OH）2D 3和未占据受体之间的简单平衡决定。肌内注射1，25（OH）2D 3后的剂量反应研究产生了双曲线，在70%受体结合率处具有明显的平台，对应于注射5 nmol 1，25（OH）2D 3。在1 nmol 1，25（OH）2D 3剂量后达到半数最大占有率，相当于1.5 ng 1，25（OH）2D 3/ml血清。根据该值，体内表观Kdin为3.7 nM，这与体外测定的值相似。1α（OH）D3剂量增加10倍导致血清1，25（OH）2D 3、占据的1，25（OH）2D 3受体或CaBP水平增加不到一倍。在所有的实验条件下，有一个正相关的受体和CaBP水平之间的关系，然而，线的斜率依赖于所选择的时间的测定部分由于滞后期CaBP诱导和其积累在细胞内。相反，血清1，25-（OH）2D 3水平和占用受体水平之间的相关性产生了一条独立于观察时间的回归线。不同维生素D代谢产物、雌激素、孕激素或皮质醇的短期和长期治疗并不影响总肠道1，25（OH）2D 3受体的水平。在正常生理条件下，配体仅占1，25（OH）_2D_3受体总数的10-15%。这些研究为进一步研究维生素D内分泌系统的生理生化参数及其临床应用提供了基础。
The dynamic equilibrium between in vivo occupied and unoccupied 1,25-dihydroxyvitamin D3[1,25(OH)2D3] receptors of the chick intestinal mucosa was investigated by the exchange assay previously reported [(1980).J. Biol. Chem.255:9534-9537]. These parameters and their correlation to biological response, i.e., the levels of intestinal vitamin D-dependent calcium binding protein (CaBP), were assessed under different physiological conditions. After a single 1,25(OH)2D3injection (3.25 nmol), occupied receptor levels increased sharply to a maximum between 1 and 2 h, followed by a rapid decline. A single dose of 1α-hydroxy-vitamin D3[1α(OH)D3], an analog that requires 25-hydroxylation for biological activity, resulted in a protracted, albeit lower, response with maximal receptor occupancy at 6 h and half maximal levels 24 h after injection. The intestinal receptor occupancy patterns mirrored the serum 1,25(OH)2D3levels after either 1,25(OH)2D3or 1α(OH)D3treatment. Additionally, time-course (half-life) of blood disappearance of 1,25(OH)2D3and occupied receptor levels were similar (1.9 and 2.3 h, respectively), suggesting that the amount of occupied 1,25(OH)2D3receptor is determined by a simple equilibrium between serum 1,25(OH)2D3and unoccupied receptors. A dose-response study after intramuscular 1,25(OH)2D3injection yielded a hyperbolic curve with an apparent plateau at 70% receptor occupancy, corresponding to 5 nmol 1,25(OH)2D3injected. Half-maximal occupancy was reached after a dose of 1 nmol 1,25(OH)2D3, corresponding to 1.5 ng 1,25(OH)2D3/ml serum. From this value the apparentKdin vivo is 3.7 nM, which is similar to that determined in vitro. A 10-fold increase in the 1α(OH)D3dose resulted in less than a doubling of the levels of serum 1,25(OH)2D3, occupied 1,25(OH)2D3receptors, or CaBP. Under all experimental conditions, there was a positive correlation between occupied receptor and CaBP levels; however, the slope of the lines depended on the times chosen for the assays due in part to the lag period for CaBP induction and its accumulation within the cell. Conversely, the correlation between serum 1,25-(OH)2D3levels and occupied receptor levels yielded a single regression line independent of the observation time. Short and long-term treatment with different vitamin D metabolites, estrogen, progesterone, or cortisol did not affect the levels of total intestinal 1,25(OH)2D3receptor. Under normal physiological conditions, only 10-15% of the total 1,25(OH)2D3receptor population was occupied by ligand. These studies provide a basis for further investigations of physiological and biochemical parameters of the vitamin D endocrine system and their clinical applications.