Calcium Regulating Hormones after Oral and Intravenous Calcium Administration

Summary: The aim of this study was to determine the changes in serum calcium concentration and in the concentrations of calcium regulating hormones after a single oral or intravenous calcium administration. Standard dosages of calcium, as used in routine patient care, were employed. Intact para thy rin, calci tonin, calcitriol, calcidiol, total calcium, ionized calcium, total protein and phosphate were determined in 12 healthy young men before and up to 8 h after oral and intravenous administration of calcium. During a fortnight there were four study days with 1000 mg calcium orally (p. o.)5 2000mg orally, 180mg calcium intravenous (i.v.) and a control day without calcium. During the study the men were on a low calcium diet. We observed a sharp increase in the calcium concentration after i.v. administration (15 min: total Ca: 4-0.48 ± 0.32 mmol/1; ionized Ca: +0.25 + 0.15 mmol/1; p < 0.01). The concentration increase after the two oral loads was nearly identical. The maximal concentration of total calcium was reached after 120 min (1000 mg: +0.1 ± 0.04 mmol/1; p < 0.001; 2000mg: +0.12 + 0.04 mmol/1; p < 0.001). There was a signif-icant increase in urinary calcium after all modes of calcium administration. Calcitonin increased significantly only after i.v. injection of calcium (+9.2 + 3.4 pmol/1; p < 0.001) whil