RATIO OF BASE-LINE LEVEL MAXIMUM LEVEL OF SERUM PTH IN PSEUDOHYPOPARATHYROIDISM AND PRIMARY HYPERPARATHYROIDISM

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.