Rubinger D, Popovtzer M M
Nephrology Services, Hadassah University Hospital, Jerusalem, Israel.
Miner Electrolyte Metab. 1987;13(5):323-32.
To further examine the interaction between the phosphaturic effects of parathyroid hormone (PTH) and extracellular volume expansion (ECVE), clearance studies were performed in chronically and acutely parathyroidectomized (PTX) rats in three sets of experiments. In the first series, two groups of chronically PTX animals (groups 1 and 2) received a PTH infusion (2 U/h). In group 1 ECVE was superimposed on the PTH infusion, while the animals in group 2 received the hormone infusion alone. In the second series the following groups of chronically PTX rats were examined: volume expanded rats (groups 3 and 4) and control normovolemic rats (group 5). A PTH bolus (5 units) was added to group 3 while group 4 underwent volume expansion alone. The third series of experiments compared the response of acutely and chronically PTX rats given a submaximal dose of PTH (1 U/h) with additional ECVE (group 6) or undergoing submaximal ECVE with additional PTH (group 7). In the first set of experiments, the PTH-ECVE rats had a higher inulin clearance (CIn) and phosphate clearance (Cp) than the animals receiving the PTH alone. The maximal fractional excretion of phosphate (Cp/CIn) was similar in both groups. In the second set, GFR was similar in the normovolemic and the volume expanded animals. The two volume expanded groups had a higher Cp/CIn than the control normovolemic animals. The maximal Cp/CIn was 0.234 +/- 0.031 in the ECVE-PTH and 0.235 +/- 0.056 in the ECVE animals (p = NS). No significant difference could be detected during the whole experiment in any variable between the volume-expanded PTH-injected (ECVE-PTH) and ECVE only rats. Acutely and chronically PTX rats responded with a similar degree of phosphaturia after ECVE superimposed on PTH infusion or after PTH superimposed on ECVE. Acutely PTX rats, however, exhibited a significantly delayed response to exogenous PTH as compared to chronically PTX animals. There was no difference in the response to ECVE between the acute and chronically PTX rats. When chronically PTX rats were exposed to submaximal ECVE, the final Cp/CIn was less than after ECVE-PTH, PTH-ECVE or PTH. These findings show that in chronically PTX rats the phosphaturic response to PTX and ECVE is not additive under conditions of maximal stimulation by PTH or ECVE. Examination of acutely PTX animals and use of a different protocol of ECVE disclose a broader spectrum of phosphaturic responses.(ABSTRACT TRUNCATED AT 400 WORDS)
为了进一步研究甲状旁腺激素（PTH）的排磷作用与细胞外液量扩张（ECVE）之间的相互作用，我们在三组实验中对慢性和急性甲状旁腺切除（PTX）大鼠进行了清除率研究。在第一组实验中，两组慢性PTX动物（第1组和第2组）接受PTH输注（2 U/h）。第1组在PTH输注的基础上叠加ECVE，而第2组动物仅接受激素输注。在第二组实验中，我们检测了以下几组慢性PTX大鼠：容量扩张大鼠（第3组和第4组）和对照正常血容量大鼠（第5组）。第3组加入一次大剂量PTH（5单位），而第4组仅进行容量扩张。第三组实验比较了给予次最大剂量PTH（1 U/h）并附加ECVE的急性和慢性PTX大鼠（第6组），以及进行次最大ECVE并附加PTH的大鼠（第7组）的反应。在第一组实验中，PTH-ECVE大鼠的菊粉清除率（CIn）和磷酸盐清除率（Cp）高于仅接受PTH的动物。两组的最大磷酸盐排泄分数（Cp/CIn）相似。在第二组实验中，正常血容量和容量扩张动物的肾小球滤过率（GFR）相似。两个容量扩张组的Cp/CIn高于对照正常血容量动物。ECVE-PTH组的最大Cp/CIn为0.234±0.031，ECVE组为0.235±0.056（p=无显著性差异）。在整个实验过程中，容量扩张并注射PTH（ECVE-PTH）组和仅进行ECVE组之间的任何变量均未检测到显著差异。在PTH输注基础上叠加ECVE或在ECVE基础上叠加PTH后，急性和慢性PTX大鼠的磷尿反应程度相似。然而，与慢性PTX动物相比，急性PTX大鼠对外源性PTH的反应明显延迟。急性和慢性PTX大鼠对ECVE的反应没有差异。当慢性PTX大鼠暴露于次最大ECVE时，最终的Cp/CIn低于ECVE-PTH、PTH-ECVE或PTH后的水平。这些发现表明，在慢性PTX大鼠中PTH或ECVE最大刺激条件下，对PTX和ECVE的磷尿反应不是相加的。对急性PTX动物的研究以及采用不同的ECVE方案揭示了更广泛的磷尿反应谱。（摘要截短至400字）
