K. Mizunashi et al., THE RELATIONSHIP BETWEEN SERUM INTACT PARATHYROID-HORMONE AND CALCIUMIN IDIOPATHIC HYPOPARATHYROIDISM, Calcified tissue international, 53(6), 1993, pp. 378-383
We studied the relationship between serum calcium (Ca) and parathyroid
hormone (PTH) in patients with idiopathic hypoparathyroidism (IHP) to
investigate the diversity of the degree of parathyroid insufficiency
and a regulation of PTH secretion by Ca in IHP. Serum intact PTH conce
ntrations ranged from < 1.0 to 10.3 pg/ml in 20 patients with IHP and
were above the detection limit in 18 (90%) patients. Serum total Ca le
vels in IHP were positively correlated with serum intact PTH (r = 0.82
4, P < 0.001), in contrast with a negative correlation between serum i
ntact PTH and Ca in 91 normal subjects (r = -0.378, P < 0.001) and abn
ormally high serum intact PTH values against hypocalcemia in five pati
ents with pseudohypoparathyroidism. In three patients with IHP, serum
intact PTH decreased in response to treatment with active vitamin D3 w
hich increased serum Ca and 1,25(OH)2D. An inverse sigmoidal relations
hip between serum ionized Ca and intact PTH was demonstrated in a pati
ent with IHP before treatment [IHP(-)] and three patients with IHP tre
ated with active vitamin D3[IHP(+)]. Peak serum intact PTH values were
reduced in IHP(-) and IHP(+). Baseline serum intact PTH was 77.0% of
the maximal level in IHP(-), 51.7-72.1% in IHP(+), and 31.1-42.3% in f
ive normal subjects. The degree of parathyroid dysfunction in IHP diff
ers from one patient to another and serum Ca levels are thought to be
determined by circulating PTH levels. Although PTH secretory reserve i
s diminished, PTH secretion is negatively regulated by Ca and is stimu
lated at baseline in patients with IHP before and during the treatment
with active vitamin D3.