Inaba M, Okuno S, Imanishi Y, Nishizawa Y, Morii H
Second Department of Internal Medicine, Osaka City University Medical School, Japan.
J Endocrinol Invest. 1992;15(9 Suppl 6):135-42.
Hypercalcemia, rather than hypocalcemia, has been observed in conjunction with severe magnesium (Mg) depletion in rat, in contrast to the development of hypocalcemia in Mg deficiency in various animal models. In the present study, a possible involvement of parathyroid hormone (PTH) in the development of hypercalcemia in rat was studied by using a newly-developed sensitive and specific radioimmunoassay system for the determination of rat PTH. In normal rat model, hypercalcemia occurred in association with a decrease of serum phosphate levels in Mg deficiency. However, serum PTH levels were not suppressed despite the occurrence of hypercalcemia, suggesting PTH as an important factor for the development of hypercalcemia. Of interest, in 5/6-nephrectomized uremic model, hypocalcemia, rather than hypercalcemia, was observed in Mg-deficient rats. Serum PTH levels seemed to be higher, but not statistically significant probably due to a small number of rats. However, infusion study clearly demonstrated that PTH secretion was significantly increased in Mg-deficient uremic rats compared with Mg-replete counterparts. The reason for an increase of serum PTH responses might be explained by Mg depletion itself in addition to a fall in serum Ca levels, because infusion study revealed that the magnitude of the stimulation of PTH secretion was increased in Mg deficiency despite the similar degrees of changes in serum Ca levels and that the set point for the suppression of PTH secretion by Ca might be altered in Mg deficiency. Taken these data together, it was strongly suggested that Mg depletion might enhance PTH secretion in rat.
与各种动物模型中镁缺乏导致低钙血症不同，在大鼠中，严重镁（Mg）缺乏与高钙血症相关。在本研究中，通过使用新开发的灵敏且特异的放射免疫分析系统来测定大鼠甲状旁腺激素（PTH），研究了PTH在大鼠高钙血症发生过程中可能的作用。在正常大鼠模型中，镁缺乏时高钙血症与血清磷酸盐水平降低相关。然而，尽管发生了高钙血症，血清PTH水平并未受到抑制，提示PTH是高钙血症发生的一个重要因素。有趣的是，在5/6肾切除的尿毒症模型中，镁缺乏的大鼠出现的是低钙血症而非高钙血症。血清PTH水平似乎较高，但可能由于大鼠数量较少而无统计学意义。然而，输注研究清楚地表明，与镁充足的大鼠相比，镁缺乏的尿毒症大鼠的PTH分泌显著增加。血清PTH反应增加的原因除了血清钙水平下降外，可能还与镁缺乏本身有关，因为输注研究显示，尽管血清钙水平变化程度相似，但镁缺乏时PTH分泌的刺激幅度增加，且镁缺乏时钙抑制PTH分泌的设定点可能改变。综合这些数据，强烈提示镁缺乏可能增强大鼠的PTH分泌。
