Plasma Calcitonin in Primary Hyperparathyroidism: Failure of C-Cell Response to Sustained Hypercalcemia*

Abstract

An acute increase in serum calcium stimulates calcitonin (CT) secretion, but the effects of chronic hypercalcemia are controversial. Histopathological studies have shown C-cell hyperplasia in primary hyperparathyroidism (1 degree HPT), although circulating levels of CT have been variously reported to be normal, elevated, or depressed. We reexamined this relationship using CT RIA in conjunction with a silica extraction technique that conveys improved sensitivity and specificity for monomeric CT. Nine men and seven women with surgically documented 1 degree HPT were studied preoperatively before and after a short calcium infusion (2 mg Ca/kg, for 5 min), as were 72 normal men and 76 normal women. Basal whole plasma immunoreactive CT and silica-extractable CT concentrations in 1 degree HPT were indistinguishable from normal, regardless of sex. In addition, the whole plasma and silica-extractable CT responses to calcium stimulation were normal or blunted in patients with 1 degree HPT. We conclude that hypercalcemia resulting from 1 degree HPT is not associated with augmented CT secretion in response to an iv calcium infusion.

Could Primary Hyperparathyroidism-Related Hypercalcemia Induce Hypercalcitoninemia?

“…The relationship between CT and hypercalcemia revealed some discrepancies: if an acute increase of serum calcium was clearly demonstrated to stimulate CT secretion, the effect of chronic hypercalcemia on CT secretion remains unclear [2,6,7,8,9,10,11,12]. …”

“…Although most of the authors found normal CT levels [7,8], others have reported basal elevated CT: in about 50% of cases in a series of 28 patients, and in men only from another series of 55 patients [9,10,11]. However, all these studies were done in a small series of patients and used polyclonal CT radioimmunoassays which are not specific of the mature CT monomer, which should explain the reported high CT levels in these series.…”

“…Acute hypercalcemia was shown to increase CT secretion by thyroid C cells, depending on both the calcium concentration and the level of calcium increase, which supports the use of calcium infusion as a stimulating CT secretion test [3,4,5]. On the contrary, the effect of chronic hypercalcemia on CT secretion remained debated: some studies found an increased CT secretion while others did not [6,7,8,9,10,11,12]. However, all these reports were done in small series of patients and have not been reconsidered by using current immunometric CT assays [6,7,8,9,10,11,12].…”

Calcitonina monomérica plasmática e hipercalcemia em pacientes portadores de neoplasia pulmonar

“…Como a CT é um hormônio liberado quando ocorre aumento dos níveis de Ca no plasma, seria de se esperar níveis elevados desse peptídio nos pacientes que se encontravam hipercalcêmicos. Mas, ao contrário, todos apresentavam-se com níveis normais ou indosáveis de CT, confirmando, assim, a perda da resposta das células C à hipercalcemia crônica já descrita por outros pesquisadores 26,27 . Estudos in vitro demonstram haver uma diminuição da sensibilidade das células C a níveis suprafisiológicos de Ca, após exposição prolongada 28 .…”

Thyrocytes, but not C cells, actively undergo growth and folliculogenesis at the periphery of thyroid tissue fragments in three-dimensional collagen gel culture

“…Effects of free Ca2+ concentration on C cell number and growth As the relationship between C cell behavior and serum Ca 2+ level has been controversial (Zabel 1976;Tiegs et al 1986;MartinLacave et al 1998), we examined the number of calcitonin-positive C cells at various free Ca 2+ concentrations. The free Ca 2+ of the complete medium was 0.39 mM (Sugihara et al 1985).…”