[Hypercalcemia and hyperphosphatemia in thyrotoxoicosis and the therapeutic effect of propranolol]

Measured levels of serum calcium, phosphate, alkaline phosphatase, and urinary hydroxyproline were measured and calcium-phosphate product was calculated in 20 hyperthyroid patients and 20 normal controls. Eleven of the patients took propranolol 160 mg per day for 28 days. We found that the serum level of calcium was higher than that of normal controls. The incidence of hypercalcaemia in hyperthyroid patients was 10%. The serum level of phosphate and the calcium-phosphate product increased (P less than 0.01). Elevation of alkaline phosphatase and bone alkaline phosphatase were also observed (P less than 0.01). The urinary hydroxyproline was also elevated (P less than 0.01). After treatment with propranolol serum calcium and triiodothyronine decreased (P less than 0.05). It is suggested that the major mechanism of hypercalcaemia and hyperphosphatemia in hyperthyroidism was increase of bone absorption stimulated by triiodothyronine. Propranolol decreased the serum level of calcium through decreasing triiodothyronine level and through beta-receptor blocking effect as well as its direct effect on bone.