Serum calcitonin-lowering effect of magnesium in patients with medullary carcinoma of the thyroid.

Abstract

A B S T R A C T The effect of magnesium chloride or magnesium sulfate infusion on circulating levels of immunoreactive calcitonin (iCT) was evaluated on nine occasions in three patients with metastatic medullary carcinoma of the thyroid. One patient was normocalcemic and had normal circulating levels of immunoreactive parathyroid hormone (iPTH), one patient was hypocalcemic and had surgical hypoparathyroidism, and one patient had mild to moderate hypercalcemia associated with bone metastases. The basal serum iPTH levels were undetectable in the latter two patients. In every instance magnesium administration produced a rapid and striking fall in circulating iCT and usually a detectable fall in serum calcium. During the hypermagnesemic state, serum iPTH fell from normal to undetectable in the patient with normal parathyroid function, while serum iPTH levels remained undetectable in the hypoparathyroid patient and in the patient with hypercalcemia associated with bone metastases. The results of these studies indicate that: (a) contrary to what has been reported in normal experimental animals, magnesium administration lowers circulating iCT in human subjects with thyroid medullary carcinoma and (b) the calcium-lowering effect produced by magnesium in patients with medullary carcinoma may, in part at least, be due to a redistribution of body calcium that is not mediated by the actions of either parathyroid hormone or calcitonin.

The effect of hypermagnesaemia on serum immunoreactive calcitonin levels in normal human subjects

“…The disparity between their findings and ours may be partly explained by the earlier time points monitored in our study and/or by the intrinsic pathophysiologic differences between pregnant women and healthy men. Anast et al (1975) demonstrated that magnesium administra¬ tion produced rapid and striking falls in the circulating iCT level in patients with thyroid medullary carcinoma. Their results might indi¬ cate an intrinsic pathophysiologic difference be¬ tween tumour cells and normal cells.…”

“…Some investi¬ gators demonstrated no significant change of se¬ rum immunoreactive CT (iCT) levels during mag¬ nesium infusion in pre-eclamptic women (Cruikshank et al 1979), whereas others found a marked increased level of serum iCT during magnesium administration (Deftos et al 1978). On the other hand, Anast et al (1975) reported that magne¬ sium administration caused a decrease in circula¬ ting iCT in patients with thyroid medullary car¬ cinoma. To study the effect of hypermagnesaemia on serum iCT levels in normal human subjects, we analysed changes in serum iCT levels, and con¬ centrations of corrected serum calcium and whole blood ionized calcium during and after iv admini¬ stration of magnesium sulphate.…”

Maintenance of normocalcemia by continuous infusion of the synthetic bovine parathyroid hormone (1–34) in parathyroidectomized rats

“…Serum Ca was measured with a Perkin-Elmer atomic absorption spectrophotometer (Perkin-Elmer Corp., Norwalk, CT). Serum iCT was measured by radioimmunoassay [6] using a goat antibody to human CT, and human CT as standards. The lower limit of detectability of this assay is 60 pg/ml.…”