The Calcemic Response to Continuous Parathyroid Hormone (PTH)(1-34) Infusion in End-Stage Kidney Disease Varies According to Bone Turnover: A Potential Role for PTH(7-84)

CONTEXT: Factors contributing to PTH resistance in dialysis patients remain elusive. OBJECTIVES: The study assessed the skeletal and biochemical response to 46 h of PTH(1-34) infusion in dialysis patients. DESIGN: The study was a prospective, controlled assessment of response to PTH(1-34). SETTING: The study was performed at the University of California, Los Angeles, General Clinical Research Center. PARTICIPANTS: Nineteen dialysis patients and 17 healthy volunteers were studied. INTERVENTION: PTH(1-34) was infused at a rate of 8 pmol/kg x h for 46 h. Bone biopsy was performed in all dialysis patients. MAIN OUTCOME MEASURES: Serum calcium, phosphorus, 1,25-dihydroxyvitamin D, PTH (four separate assays), and FGF-23 were determined at baseline and h 7, 23, 35, and 46 of the infusion. RESULTS: Serum calcium levels rose in healthy volunteers (9.2 +/- 0.1 to 11.9 +/- 0.3 mg/dl; P < 0.01) and in dialysis patients with adynamic/normal bone turnover (9.0 +/- 0.3 to 10.7 +/- 0.7 mg/dl; P < 0.05) but did not change in dialysis patients with high bone turnover. Serum phosphorus levels declined in healthy volunteers (3.9 +/- 0.1 to 3.5 +/- 0.1 mg/dl; P < 0.05) but increased in all dialysis patients (6.7 +/- 0.4 to 8.0 +/- 0.3 mg/dl; P < 0.05). Full-length PTH(1-84) declined in all subjects; however, PTH(7-84) fragments declined only in healthy subjects and in dialysis patients with normal/adynamic bone but remained unchanged in dialysis patients with high bone turnover. CONCLUSIONS: The skeleton of dialysis patients with high bone turnover is resistant to the calcemic actions of PTH. PTH(7-84) may contribute to this phenomenon.