Silicon metabolism. II. Renal handling in chronic renal failure patients.

In 36 patients suffering from chronic renal failure (mean creatinine clearance 26 ml/min), serum silicon levels were significantly increased (mean 0.52 microgram/ml compared with 0.265 microgram/ml in normals; p less than 0.005). Urinary silicon excretion per 24 h was significantly decreased (15.71 mg/24 h compared with 21.4 mg/24 h in normals; p less than 0.001). Fractional excretion of silicon (FESi) was significantly increased in chronic renal failure (p less than 0.001), with overall tubular secretion of silicon in 33% of patients. Urinary excretion of silicon was significantly related to urinary calcium excretion (p less than 0.0001) urinary magnesium excretion (p less than 0.0001) creatinine clearance (p less than 0.05) and sodium excretion (p less than 0.05). It is suggested that urinary silicon is in the form of orthosilicate, principally bound to calcium and magnesium; and that in chronic renal failure the increase in FESi, and the decrease in absorbed Si from the gastrointestinal tract, moderate the increase in plasma silicon levels and prevent excessive entry of silicon into the tissues.