Parathyroid hormone-related peptide plasma concentrations in patients on hemodialysis

BACKGROUND: Uremic patients develop hyperplasia of the parathyroid glands due to disturbances in the mineral metabolism. The hyperplastic parathyroids are associated with significant expression of parathyroid hormone (PTH)-related peptide (PTHrP). PTHrP has been shown to have an autocrine/paracrine function in the parathyroids, but it is still uncertain if PTHrP is a secretory product of the gland and thereby possess endocrine actions. In cells of severe adenomatous secondary hyperparathyroidism PTHrP and PTH have been found to be co-localized in the same secretory granules. PTH and PTHrP act through the same receptor, the PTH1R, and it has been shown experimentally that PTHrP enhances the PTH secretory response to hypocalcemia, indicating a link between the two hormones. METHODS: Together with a number of parameters involved in mineral homeostasis plasma PTHrP was measured before hemodialysis in 90 patients and in 15 healthy subjects. Plasma PTH was determined in order to examine the possible relationship between the two peptides. RESULTS: In hemodialysis patients mean plasma PTHrP, 4.2 +/- 2.1, was significantly lower than that of healthy subjects, 8.3 +/- 1.1 pmol/L, p <0.0001. No relationship was found between plasma PTHrP and PTH in hemodialysis patients. Gender, PTX, specific treatments and diagnoses had no impact on PTHrP concentrations. CONCLUSION: Thus PTHrP is measurable in hemodialysis patients, but its secretion might not be part of a regulated mineral homeostatic process and may not derive from the uremic hyperplastic parathyroid glands