Effect of intravenous calcium on urinary cyclic adenosine-3',5'-monophosphate and hydroxyproline in children with hypoparathyroidism

Abstract

Abstract. The effect of iv calcium on the urinary excretion of total adenosine-3',5',-monophosphate (cAMP) and total hydroxyproline (OH-P) was investigated in 5 children with parathyroid hormone (PTH)-deficient and PTH-resistant hypoparathyroidism, two of them being normocalcaemic during the study, in comparison to 4 healthy and 8 epileptic children and adolescents. Eighteen mg/kg body weight calcium, infused over 3 h, induced a decrease of cAMP to (mean ± sd) 82.1 ± 2.5% of the baseline value in controls and to 69.8 ± 9.7% in epileptic patients with an inverse correlation to the relative increase of serum calcium after the infusion in both groups (r = −0.75, P < 0.01). In contrast, the cAMP excretion increased after calcium load in the 5 hypoparathyroid children to 118.7 ± 14.9% of baseline despite a comparable serum calcium increase. OH-P decreased to (mean ± SD) 48.0 ± 6.8% of baseline in controls, 48.2 ± 12.7% in the epileptic patients and 39.4 ± 9.8% in the children with hypoparathyroidism, the differences between the three groups being statistically not significant. It is concluded that the simple measurement of urinary cAMP before and after calcium infusion may provide a diagnostic tool to identify hypoparathyroid patients even in the normocalcaemic state. In contrast, the measurement of the calcium-induced suppressibility of OH-P does not discriminate these patients from subjects with normal parathyroid function.