FGF-23 Suppressibility by Calcitonin

Introduction: Based on our experience with calcitonin as an FGF-23 suppressive agent in a patient with an FGF-23 producing tumor we hypothesize that calcitonin may be a physiologically important regulator of FGF-23 production and secretion in healthy humans. Aim: In this study we wish to examine the FGF-23 suppressive effects of calcitonin in healthy men. Study Design: placebo-controlled, cross-over study Method: All twelve subjects are examined on two occasions, once after exposure to placebo 1 ml NaCl 0.9% subcutaneously, and once following calcitonin 200 IU/ml subcutaneously On both occasions frequent bloodsampling will take place, out an indwelling catheter in de forearm vein. Sampling times: -15, 0, 60, 120, 240, 360, and 480 minutes Mealtimes: Calcium and Phosphate intake standardized on both occasions All samples are analyzed for FGF-23, using a C-terminal FGF-23 ELISA kit (Immunotopics, San Clemente, USA) that measures intact and C-terminal fragments of FGF-23, and one that measures only intact FGF-23 Samples obtained at T-15, T0, T240 and T480 are stored for later analysis of Ca, albumin, PO4, PTH, 25-OHD and 1,25-OHD Endpoint: A change of 25% in de serum FGF-23 levels in response to a single subcutaneous injection of calcitonin 200 IU.

A change of 25% in de serum FGF-23 levels in response to a single subcutaneous injection of calcitonin 200 IU.

Inclusion Criteria: Healthy man, who are between 20-55 years old, and have a BMI 20-27 kg/m2. Exclusion Criteria: Serum creatinin >100 mmol/L, or glomerular filtration rate <80 ml/min. Abnormal serum Ca, PO4, albumin, 25-OH vitamin D, or PTH levels. Any medication.