Altered diurnal regulation of blood ionized calcium and serum parathyroid hormone concentrations during parenteral nutrition

Background: Little is known about parathyroid gland function in patients re ceiving total parenteral nutrition (TPN). Objective: Our objective was to determine whether parathyroid gland functio n is abnormal in TPN recipients. Design: Six patients with a mean (+/- 1 SD) age of 45.5 +/- 8.0 y who had b een receiving TPN for 18.7 +/- 2.8 y underwent bone TPN for 18.7 +/- 2.8 y underwent bone biopsy, bone mass measurements with dual-energy X-ray absorp tiometry, and dynamic tests of parathyroid gland function. Diurnal variatio ns in blood ionized calcium (iCa(2+)) and serum parathyroid hormone (PTH) c oncentrations were also assessed. Results were compared with those of healt hy volunteers. Results: Bone mass and bone formation were subnormal in all patients. Basal serum PTH concentrations were moderately higher in the TPN recipients than in healthy volunteers, and values obtained every 30 min over 24 h were sig nificantly higher (P < 0.001) in TPN recipients (5.0 +/- 0.9 pmol/L) than i n healthy volunteers (2.6 +/- 0.6 pmol/L). The percentage increase in serum PTH during citrate-induced hypocalcemia was lower in the TPN recipients, c onsistent with secondary hyperparathyroidism. Evening infusions of calcium- containing TPN eliminated the nocturnal rise in serum PTH, increased the am plitude of change for iCa(2+) and PTH over 24 h, increased the orderliness of change for iCa(2+) and PTH as measured by approximate entropy (ApEn), an d enhanced the synchrony of change between iCa(2+) and PTH. Treatment for 1 0 d with calcium-free TPN restored the nocturnal rise in serum PTH and incr eased ApEn for PTH. ApEn for iCa (2+) remained low, suggesting that a compo nent of nutrient solutions, bur not calcium per se, enhances the regularity of PTH release in TPN recipients. Conclusion: Parathyroid gland function is abnormal in long term TPN recipie nts, which may contribute to disturbances in bone metabolism.