Degradation of radioiodinated porcine and human synthetic calcitonins by sera of different species

Monomeric calcitonin secretion in infants with congenital hypothyroidism

We have determined CT levels in whole serum (iCT) and by an extraction method (exCT) in 25 infants affected by congenital hypothyroidism (CH)--11 athyreotic and 14 dysgenetic--at age 25 days, before the institution of therapy, and at age 2 years. In hypothyroid patients at age 25 days the iCT and exCT levels were similar to those found in controls of the same age. At age 2 years the iCT and exCT levels decreased in both groups of patients. However, whereas the levels of iCT in hypothyroids were similar to those found in controls of the same age, the levels of exCT were significantly lower in hypothyroids than in controls; moreover they were significantly lower in athyreotic than in dysgenetic patients. At this age, after calcium infusion, exCT levels significantly increased in dysgenetic but not in athyreotic patients. We hypothesize that CT deficiency in CH is due to increased degradation of human CT by the substitutive therapy, which, stimulating proteolytic enzymes, destroys the biologic activity of CT. An extraction procedure improves the sensitivity and specificity of the CT assay and it must be used when CT deficiency is suspected. In addition we suggest that the measurement of exCT levels after Ca infusion might be useful to distinguish dysgenetic from athyreotic patients.

Plasma kinetics and urinary excretion of exogenous human and salmon calcitonin in man

The metabolism and the urinary excretion of synthetic human and salmon calcitonin-(1--32) [hCT-(1--32), sCT-(1--32)] administered by constant infusions for 240 min were investigated in eight normal subjects. On gel filtration of plasma obtained during the infusions mainly intact hCT-(1--32) and sCT-(1--32) were recognized with homologous radioimmunoassay systems. During constant infusions to equilibrium of 0.04 mg hCT-(1--32) and sCT-(1--32), the metabolic clearance rates (MCR) amounted to 8.4 +/- 1.1 and 3.1 +/- 0.1 ml/kg per min, respectively (P less than 0.01). When hCT-(1--32) was infused at rates of 1 and 4 mg/240 min, the MCR were lower than with 0.04 mg hCT-(1--32), but still higher than with 0.04 mg sCT-(1--32). The half-lives of disappearance of hCT-(1--32) were faster compared to sCT-(1--32), but the difference was not statistically significant. The urinary clearance of hCT-(1--32) determined during the 1 and 4 mg/240 min infusions of hCT-(1--32), as well as of sCT-(1--32) determined during the 0.04-mg infusions of sCT-(1--32) was about 0.1% of the MCR. The half-lives of disappearance of hCT- and sCT-(1--32) incubated in vitro in plasma and urine ranged from 17 to more than 72 h, and the degradation did not affect our calculations of the metabolic breakdown of exogenous CT in vivo.