Calcitriol therapy and calcium-regulated PTH secretion in patients with secondary hyperparathyroidism.
Calcitriol lowers serum parathyroid hormone (PTH) levels in patients with secondary hyperparathyroidism, but its effect on calcium-regulated PTH release remains controversial. Thus 11 patients with secondary hyperparathyroidism underwent dynamic tests of parathyroid function before and after 4 mo of intermittent calcitriol therapy. Serum calcitriol levels rose from 8 +/- 1 to 55 +/- 9 (SE) pg/ml, P < 0.01, serum total and ionized calcium levels increased, and serum PTH levels decreased from 584 +/- 154 to 154 +/- 31 pg/ml, P < 0.05. The maximum increase in serum PTH during hypocalcemia did not differ before (248 +/- 78 pg/ml) or after (280 +/- 100 pg/ml) treatment, but the increase in PTH, expressed as a percentage of preinfusion values, was greater after treatment (329 +/- 73 vs. 132 +/- 10%, P < 0.05). The decreases in serum PTH during calcium infusions did not differ before (70 +/- 5%) or after (73 +/- 5%) therapy, and the set point for PTH release did not change (1.20 +/- 0.03 vs. 1.23 +/- 0.01 mmol/l, not significant). Calcitriol modifies PTH secretion during hypocalcemia in secondary hyperparathyroidism without affecting the set point for PTH release; although calcitriol lowers serum PTH levels, it may also restore the secretory reserve of hyperplastic parathyroid tissues during hypocalcemia.
Ramirez
J A
JA
Department of Pediatrics, School of Medicine, University of California at Los Angeles 90024.
Goodman
W G
WG
Belin
T R
TR
Gales
B
B
Segre
G V
GV
Salusky
I B
IB
D000293:Adolescent; D002117:Calcitriol / Q000494:pharmacology / Q000627:therapeutic use*; D002118:Calcium / Q000097:blood*; D002125:Calcium Gluconate / Q000494:pharmacology; D002951:Citrates / Q000494:pharmacology; D019343:Citric Acid; D005260:Female; D006801:Humans; D006962:Hyperparathyroidism, Secondary / Q000188:drug therapy / Q000378:metabolism*; D008297:Male; D010281:Parathyroid Hormone / Q000378:metabolism*
D002951:Citrates; D010281:Parathyroid Hormone; D019343:Citric Acid; D002117:Calcitriol; D002125:Calcium Gluconate; D002118:Calcium