Effect of parathyroid hormone (hPTH[1-34]) infusion on serum 1,25-dihydroxyvitamin D and parathyroid hormone in normal women

Abstract

Calcium absorption declines with age. Because 1,25-dihydroxyvitamin D (1,25(OH)2D) is the major hormone controlling calcium absorption, changes in vitamin D metabolism may account for the malabsorption of aging. Serum levels of 1,25(OH)2D have been reported to either decrease or remain unchanged with age. To assess the effect of aging on renal production of 1,25(OH)2D, we evaluated the response of renal 25OHD 1 alpha hydroxylase to human parathyroid hormone (hPTH(1-34) stimulation in 119 women ages 25-83 years. In this population, baseline serum 25OHD and 1,25(OH)2D values did not significantly change with age, but serum iPTH (r = 0.44; p < 0.001) and serum creatinine (r = 0.31; p < 0.01) increased with age. However, the stimulatory activity of hPTH(1-34) on the renal production of 1,25(OH)2D declined with age (r3 = -0.36; p < 0.001) and was most apparent after age 75, being 50% less than that of younger women. Besides age, the production of 1,25(OH)2D was found to be dependent on baseline serum iPTH (r = -0.31; p < 0.0001). Administration of hPTH(1-34) led to suppression of endogenous PTH, and suppressibility of endogenous PTH declined with age (r = 0.53; p < 0.0001). The increase in serum PTH and decreased suppressibility of PTH with age could be due to mild secondary hyperparathyroidism. The increase in PTH with age is probably responsible for maintaining normal serum 1,25(OH)2D levels in elderly subjects; however, decreased metabolism of 1,25(OH)2D in the elderly could also maintain normal serum 1,25(OH)2D levels.

Acute changes in serum osteoprotegerin and receptor activator for nuclear factor-κB ligand levels in women with established osteoporosis treated with teriparatide

“…Similar reduction in endogenous PTH was observed acutely after TPTD infusion in normal (22) and osteoporotic women (23). iPTH decrease can be attributed to the suppressive effect of TPTD.…”

Endogenous Intact PTH is Suppressed during Teriparatide (rhPTH 1-34) Administration in Postmenopausal Women with Established Osteoporosis

“…Similar decline in endogenous ΡΤΗ was observed acutely after TPTD administration in normal [3] and osteoporotic women [4]. iPTH decrease has to be attributed to the suppressive effect of TPTD, as it seems that the administration of 20 µg TPTD daily is sufficient enough to inhibit endogenous iPTH release from the parathyroid glands; furthermore the aminoterminal end of PTH is probably the part of the molecule that exerts the negative feedback.…”

“…In the published literature there is very little evidence on acute changes in endogenous intact PTH (iPTH) levels after TPTD administration [3,4]; on the other hand, there are no data at all on iPTH changes during long-term treatment. The primary aim of this prospective study was to evaluate the acute and chronic effects of intermittent TPTD administration in serum iPTH levels in postmenopausal women with established osteoporosis.…”

Parathyroid hormone stimulation of the renal 25-hydroxyvitamin D-1α-hydroxylase—Effect of age and free radicals

“…In humans, two studies have shown that the capacity of PTH to increase serum 1,25(OH) 2 D levels declines with age [3,4]. In rats, with maturation and aging, the capacity of PTH to stimulate renal 1,25(OH) 2 D production also declines.…”