Role of uremia, brain calcium, and parathyroid hormone on changes in electroencephalogram in chronic renal failure

Acute uremia is associated with increased calcium (Ca) in brain and changes in electroencephalogram (EEG), and both derangements are related to excess parathyroid hormone (PTH). Also changes in EEG in patients with chronic renal failure (CRF) correlated directly with blood levels of PTH, and fall in PTH was followed by improvement in EEG. We examined whether chronic uremia per se has an effect on brain calcium or EEG. Uremia was produced by 5/6 nephrectomy and maintained for 32-70 wk in seven thyroparathyroidectomized (TPTX) and seven control dogs. There were no differences in creatinine clearance and serum electrolytes except for HCO3, which was lower in control animals (P less than 0.01). Serum PTH was undetectable in TPTX dogs but was significantly elevated in control animals (32.3 +/- 3.3 mu leq /ml). Calcium in gray and white matter was significantly increased in both groups but much higher in control animals. The percent waves of less than 7 Hz in EEG were similar in both groups prior to uremia (TPTX 4.6 +/- 0.8 vs. control 4.2 +/- 0.5%) but remained unchanged in TPTX animals and increased significantly in control dogs (19.0 +/- 1.3%) after uremia. These data suggest that CRF per se is associated with marked rise in Ca in both gray and white matter and increment is higher in the presence of PTH. Disturbance in EEG in a state of CRF requires the presence of excess PTH and is prevented despite increased Ca in brain if hyperparathyroidism is not allowed to develop.