AGING ALTERS CALCIUM REGULATION OF SERUM CONCENTRATION OF PARATHYROID-HORMONE IN HEALTHY-MEN

We examined the effect of aging on the relationship between the concen trations of blood ionized calcium and of serum parathyroid hormone (PT H) in 22 healthy men [9 elderly (age 74 +/- 2 yr) and 13 young (age 39 +/- 1 yr)] in whom the glomerular filtration rate was >70 ml/min. Thr oughout a 24-h period, serum concentrations of PTH in the elderly men were twice those in the young men, whereas blood ionized calcium did n ot differ between the two groups. With intravenous infusion of calcium gluconate, the minimum PTH concentration was two- to threefold higher in the elderly men. With infusion of NaEDTA, the maximum PTH concentr ation was 20% higher in the elderly men. The calcium set point for PTH release was higher in the elderly than in the young men (4.71 +/- 0.0 4 vs. 4.54 +/- 0.03 mg/dl, respectively, P < 0.005). In these healthy men, the age-related increase in serum PTH could not be attributed to a sustained decrease in concentration of either blood ionized calcium or 1,25-hydroxyvitamin D. These findings suggest that, with aging, the relationship between calcium and PTH is altered such that at any give n level of calcium, the concentration of PTH is higher.