The Miscible Calcium Pool in Metabolic Bone Disease—in Particular, Acromegaly

Abstract

The miscible calcium pool and the 24-hr plasma specific activity were studied by means of a sustained intravenous infusion of calcium⁴⁵ in 51 patients, some of whom had various metabolic bone diseases. In normal subjects, the estimated rapidly miscible pool was 34.1 ±1.7 mg/kg body weight, and the 24-hr plasma activity was 19.5 ±3.5% total dose/g calcium. Patients with Paget's disease of the bone and patients with primary hyperparathyroidism had increased miscible calcium pool and decreased 24-hr plasma specific activity values. In patients with hypoparathyroidism and in patients with Cushing's syndrome, the reverse changes were found. Patients with osteomalacia secondary to renal disease had markedly increased miscible calcium pools, while patients with osteoporosis,urolithiasis, sarcoidosis, milk-alkali syndrome or vitamin D intoxication revealed varying values partially overlapping the normal range. The increased miscible calcium pool and decreased 24-hr plasma specific activity found in active acromegaly was of particular interest and is helpful in elucidating the pathogenesis of bone disease in this condition. It is suggested that the “osteoporosis” of acromegaly is due at least in part to the prolonged negative calcium balance secondary to hypercalciuria.