title: Role of parathyroid hormone in mediating nocturnal and age-related increases in bone resorption.
abstract: PTH has been postulated to play a role in both nocturnal and age-related increases in bone resorption. We tested this hypothesis directly in 10 young (ages 24-35 yr) and 10 elderly (ages 71-78 yr) normal women by measuring the cross-linked N-telopeptide of type I collagen (NTx), a marker for bone collagen breakdown, in 4-h urine collections before and during suppression of PTH secretion by a 24-h iv infusion of calcium. Serum ionized calcium and PTH levels were also measured every 2 h before and during the infusion. In both groups of women, serum PTH levels and urinary NTx excretion followed a circadian pattern before calcium infusion (analysis of variance, P = 0.0001) with peaks in the afternoon and at night for PTH and at night for urinary NTx. During the calcium infusion, the nocturnal urinary NTx excretion peak persisted (P = 0.0001), despite elimination of both PTH peaks. Urinary 24-h NTx excretion (nanomoles per millimoles of creatinine) at baseline was higher in the elderly women (mean +/- SEM, 25.7 +/- 2.1) than in the young women (19.3 +/- 1.7) (P < 0.01), and the decrease during calcium infusion was greater (7.5 +/- 1.9 vs. 4.1 +/- 1.5, P < 0.05). Therefore, the increase in serum PTH levels with age is one of the major factors responsible for the age-related increase in bone resorption. PTH does not mediate the circadian pattern of bone resorption but does play a role in setting the absolute level of bone resorption at which this pattern occurs.
authors.affiliation: Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: G A
authors.initials: GA
authors.lastname: Ledger
authors.forename: M F
authors.initials: MF
authors.lastname: Burritt
authors.forename: P C
authors.initials: PC
authors.lastname: Kao
authors.forename: W M
authors.initials: WM
authors.lastname: O'Fallon
authors.forename: B L
authors.initials: BL
authors.lastname: Riggs
authors.forename: S
authors.initials: S
authors.lastname: Khosla
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001862:Bone Resorption / Q000503:physiopathology*; D002118:Calcium / Q000494:pharmacology* / Q000652:urine; D002940:Circadian Rhythm; D003094:Collagen / Q000652:urine; D024042:Collagen Type I; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D010281:Parathyroid Hormone / Q000037:antagonists & inhibitors / Q000097:blood / Q000502:physiology*; D010455:Peptides / Q000652:urine
chemical_list: D024042:Collagen Type I; D010281:Parathyroid Hormone; D010455:Peptides; C052929:collagen type I trimeric cross-linked peptide; D003094:Collagen; D002118:Calcium