Journal of Clinical Endocrinology & Metabolism, Vol 79, 211-216, Copyright © 1994 by Endocrine Society

ARTICLES

Abnormalities of parathyroid hormone secretion in elderly women that are reversible by short term therapy with 1,25-dihydroxyvitamin D3

GA Ledger, MF Burritt, PC Kao, WM O'Fallon, BL Riggs and S Khosla
Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota 55905.

Serum PTH concentrations increase with aging and may play an important causal role in age-related bone loss. To better define possible PTH secretory abnormalities with aging, we studied 10 young (aged 27-34 yr) and 10 elderly (aged 71-77 yr) women using sequential infusions of calcium and EDTA. To assess possible age-related resistance of PTH secretion to modulation by 1,25-dihydroxyvitamin D [1,25-(OH)2D], the infusions were repeated after 1 week of oral 1,25-(OH)2D3 therapy (1 microgram/day). Baseline serum intact PTH concentrations were higher in the elderly compared to the young women (mean +/- SEM, 3.8 +/- 0.5 vs. 2.7 +/- 0.4 pmol/L; P = 0.03). In addition, the elderly women had a significantly higher maximal PTH response to hypocalcemia compared to the young women (16.6 +/- 1.1 vs. 12.8 +/- 1.0 pmol/L; P = 0.03). The elderly women also had a greater nonsuppressible component of PTH secretion (0.8 +/- 0.1 vs. 0.4 +/- 0.1 pmol/L; P < 0.001). The set- point for PTH secretion, however, was identical in the elderly and young women (1.18 +/- 0.01 vs. 1.19 +/- 0.01 mmol/L; P = NS). After 1,25-(OH)2D3 administration, both groups had similar reductions in baseline and maximally stimulated PTH levels, indicating that elderly women have normal responsiveness to 1,25-(OH)2D3 suppression of PTH secretion. In addition, maximally stimulated PTH levels in the 1,25- (OH)2D3-treated elderly women decreased to the pretreatment values of young women (13.3 +/- 1.1 vs. 12.8 +/- 1.0 pmol/L; P = NS). thus, elderly women have greater basal, maximal, and nonsuppressible levels of PTH secretion, without alterations in the set-point. These abnormalities are similar to those found in patients with secondary hyperparathyroidism and parathyroid hyperplasia. Further, the abnormal PTH secretory dynamics in elderly women are reversible by short term 1,25-(OH)2D3 therapy.

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