title: Dynamics of PTH secretion in hemodialysis patients as determined by the intact and whole PTH assays.
abstract: BACKGROUND
  Renal hyperparathyroidism is assessed by measurement of parathyroid hormone (PTH) levels. The intact PTH assay (I-PTH) not only reacts with 1-84 PTH but also with large, truncated fragments of non-1-84 PTH. Because the whole PTH assay (W-PTH) is specific for 1-84 PTH, non-1-84 PTH is determined by subtracting W-PTH from I-PTH values. These large circulating PTH fragments may exert a hypocalcemic effect by contributing to skeletal resistance to 1-84 PTH.
  
  
  METHODS
  The dynamic secretion of both 1-84 PTH and non-1-84 PTH was evaluated during the induction of hypo- and hypercalcemia in eight hemodialysis patients.
  
  
  RESULTS
  The basal ionized calcium concentration was 1.23 +/- 0.03 mmol/L at which time I-PTH, W-PTH, and non-1-84 PTH values were 276 +/- 78 pg/mL, 164 +/- 48 pg/mL, and 102 +/- 28 pg/mL, respectively. The induction of hypo- and hypercalcemic changes resulted in a sigmoidal response for all three PTH moieties, I-PTH, W-PTH, and non-1-84 PTH. During hypocalcemia, maximal values of W-PTH were greater than those of non-1-84 PTH. But during hypercalcemia, minimal values of W-PTH and non-1-84 PTH were similar. Neither the set points nor the basal/maximal ratios for W-PTH, I-PTH, and non-1-84 PTH were different. At the baseline ionized calcium concentration, the W-PTH (1-84 PTH)/non-1-84 PTH ratio was 1.53 +/- 0.15. Changes in ionized calcium resulted in a sigmoidal relationship with hypocalcemia, increasing this ratio to a maximum of 2.01 +/- 0.30 and hypercalcemia decreasing this ratio to a minimum of 1.18 +/- 0.15 (P < 0.01 vs baseline for both hypo- and hypercalcemia).
  
  
  CONCLUSIONS
  Although acute changes in serum calcium produce similar secretory responses in 1-84 PTH and non-1-84 PTH, the secretory responses are not proportional for these PTH moieties. Changes in the serum calcium concentration modulate the ratio of 1-84 PTH/non-1-84 PTH in a sigmoidal pattern with hypocalcemia maximizing this ratio. Whether changes in the 1-84 PTH/non-1-84 PTH ratio specifically modulate the calcemic action and other biologic effects of 1-84 PTH remain to be determined.
authors.affiliation: Nephrology Service, Reina Sofia University Hospital, Cordoba, Spain. rasol@inicia.es
authors.forename: Rafael
authors.initials: R
authors.lastname: Santamaria
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Almaden
authors.forename: Arnold
authors.initials: A
authors.lastname: Felsenfeld
authors.forename: Alejandro
authors.initials: A
authors.lastname: Martin-Malo
authors.forename: Ping
authors.initials: P
authors.lastname: Gao
authors.forename: Tom
authors.initials: T
authors.lastname: Cantor
authors.forename: Pedro
authors.initials: P
authors.lastname: Aljama
authors.forename: Mariano
authors.initials: M
authors.lastname: Rodriguez
mesh_terms: D000368:Aged; D002118:Calcium / Q000097:blood; D006801:Humans; D006934:Hypercalcemia / Q000378:metabolism; D006962:Hyperparathyroidism, Secondary / Q000378:metabolism; D007676:Kidney Failure, Chronic / Q000378:metabolism* / Q000628:therapy; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood* / Q000378:metabolism*; D010758:Phosphorus / Q000097:blood; D006435:Renal Dialysis
chemical_list: D010281:Parathyroid Hormone; D010758:Phosphorus; D002118:Calcium