K. Mizunashi et al., RATIO OF BASE-LINE LEVEL MAXIMUM LEVEL OF SERUM PTH IN PSEUDOHYPOPARATHYROIDISM AND PRIMARY HYPERPARATHYROIDISM, Calcified tissue international, 62(2), 1998, pp. 99-103
The ratio of baseline level/maximum level of serum parathyroid hormone
(PTH) is high in PTH-deficient hypoparathyroidism and it decreases af
ter vitamin D-3 treatment. There is a reversed sigmoidal relationship
between the ratio and baseline serum Ca level. In this study, we furth
er investigated the value of this ratio as a parameter of Ca-dependent
changes of serum PTH in hyperparathyroid subjects, As in PTH-deficien
t hypoparathyroidism, the ratio in pseudohypoparathyroidism was high b
efore vitamin D-3 treatment and it decreased after 1,25(OH)(2)D-3 trea
tment. The increased ratio may reflect the stimulated baseline PTH sec
retion from parathyroid cells perceiving the decrease in baseline extr
acellular Ca level. The points plotting the ratio against baseline ser
um Ca level were on the regression curve deduced from the data in PTH-
deficient hypoparathyroidism. This result indicates that the relations
hip between the ratio and the baseline extracellular Ca level is unrel
ated to the variation in maximum secretion. The sigmoidal changes of s
erum PTH in patients with parathyroid adenoma were classified as follo
ws. The first was with the upward and rightward curve shift, the secon
d was only with the rightward curve shift, and the third was with the
rightward curve shift, the increased minimum serum PTH, and the increa
sed baseline/maximum ratio of serum PTH. These findings suggest that t
he decreased suppressibility of PTH secretion and the stimulated basel
ine secretion may develop without the increase in maximum secretion in
some cases with parathyroid adenoma. In conclusion, the ratio of base
line level/maximum level of serum PTH may unfold a new aspect of secre
tion abnormality of parathyroid glands in several forms of parathyroid
disorders.