Aspects of phosphate metabolism in kidney disease. The pre-eminence of extrarenal factors.

In 20 patients with chronic kidney disease, both with normal GFR and various degrees of renal insufficiency, an i.v. infusion of a standard phosphate solution was performed. The TmPO 4, the TmPO 4/GFR and the distribution spaces of phosphate into the body fluids were investigated. Seven patients with GFR less than 30 ml/min (and 13 more patients with chronic renal disease and comparable degree of renal failure) and 20 controls were submitted to muscle biopsy for study of cell phosphate concentration. A direct relationship between GFR and TmPO 4/GFR values was found. On the contrary, GFR values appeared to be indirectly correlated to phosphate distribution spaces. Moreover, in patients with GFR less than 30 ml/min, a significant increase in the phosphate content of muscle cells was observed. This behavior is believed to depend on the circulating levels of parathyroid hormone. The increased cell uptake of phosphate could counteract, within certain limits, the reduced renal clearance of phosphate in patients with chronic renal insufficiency.