Plasma levels of parathyroid hormone (1-84) whole molecule and parathyroid hormone (7-84)-like fragments in pseudohypoparathyroidism type I.
PTH (7-84) has antagonistic effects on the calcemic and phosphaturic actions of PTH (1-84) whole molecule (bioPTH). Human plasma contains bioPTH and PTH (7-84)-like fragments. Using bioPTH-specific and nonspecific assays, we found that the patients with pseudohypoparathyroidism (PHP) type I with PTH-resistant hypocalcemia and hyperphosphatemia had the increased plasma levels of bioPTH and PTH (7-84)-like fragments than normal subjects (26.8 +/- 13.2 vs. 2.37 +/- 0.75 pmol/liter, P < 0.01 and 16.2 +/- 8.8 vs. 0.82 +/- 0.47 pmol/liter, P < 0.01, respectively). Calcitriol treatment increased phosphaturic response to PTH (1-34) (P < 0.05), and there was a negative correlation between phosphaturic response and the PTH levels (P < 0.05). These results suggested that the increased bioPTH and PTH (7-84)-like fragment levels may be related to the impaired phosphaturic response to PTH (1-34) in PHP type I. We also examined bioPTH-calcium dynamics in PHP type Ib patients and found that set-point calcium was 0.928 +/- 0.045 mmol/liter and the baseline to maximal ratio of bioPTH was 0.96 +/- 0.04. Calcitriol treatment increased set-point calcium to 1.129 +/- 0.028 mmol/liter (P < 0.01) and suppressed baseline to maximal ratio of bioPTH to 0.35 +/- 0.21 (P < 0.01). These bio-PTH calcium dynamics studies revealed the maximally stimulated baseline PTH secretion in PHP type Ib and demonstrated the effects of calcitriol on PTH-calcium curve shift and the degree of relative stimulation of baseline secretion.
Hatakeyama
Yuriko
Y
Division of Laboratory Medicine, Tohoku University School of Medicine, Aoba-ku, Sendai 980-8574, Japan.
Mizunashi
Kazutoshi
K
Furukawa
Yohtaro
Y
Yabuki
Shigemitsu
S
Sato
Yumi
Y
Igarashi
Teruo
T
D000293:Adolescent; D002117:Calcitriol / Q000008:administration & dosage; D002118:Calcium / Q000097:blood; D004351:Drug Resistance; D005260:Female; D006801:Humans; D006996:Hypocalcemia / Q000188:drug therapy / Q000209:etiology; D008297:Male; D010281:Parathyroid Hormone / Q000008:administration & dosage / Q000097:blood*; D010446:Peptide Fragments / Q000008:administration & dosage / Q000097:blood*; D010710:Phosphates / Q000097:blood / Q000652:urine; D011547:Pseudohypoparathyroidism / Q000097:blood* / Q000150:complications; D012016:Reference Values
D010281:Parathyroid Hormone; D010446:Peptide Fragments; D010710:Phosphates; C414937:parathyroid hormone (7-84); D002117:Calcitriol; D002118:Calcium