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SUMMARY
In an investigation of the possible role of calcitonin in the metabolism of glycosaminoglycans it was found that the hormone increased the rate of disappearance from serum of [35S]sulphate injected into rats. No excessive deposition of radioactive sulphate was found in bone, kidney, liver or ventricular myocardium of calcitonin-treated rats.
Calcitonin also rapidly lowered serum inorganic sulphate levels. Both effects were prevented by previous nephrectomy, leading to the conclusion that calcitonin acts on the kidney to promote the excretion of inorganic sulphate.
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SUMMARY
The distribution and localization of 125I-labelled bovine parathyroid hormone was studied by radioautography in adult rats. The principal site of localization was the proximal convoluted tubule of the kidney. Light and variable localization was present in the liver, but no significant amount of label was found in muscle, spleen, bone or articular cartilage. The localization of this labelled compound in the proximal convoluted tubule suggests that this region degrades 125I-labelled parathyroid hormone.
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SUMMARY
When [125I]calcitonin was injected intravenously into rats the major site of accumulation of radioactivity was the liver, whereas [125I]parathyroid hormone was localized chiefly in the kidney.
The distribution of [125I]bovine serum albumin and of Na [125I] was studied for comparison. Although most of the radioactivity of [125I]calcitonin was found in the soluble fractions of liver and kidney, significant binding to liver microsomes occurred. This fraction also bound an appreciable amount of the radioactivity of [125I]parathyroid hormone. The uptake of [125I]calcitonin by liver could be inhibited by the simultaneous injection of unlabelled calcitonin, but not by that of parathyroid hormone, insulin or adrenocorticotrophic hormone.
These results indicate a role for the liver and kidney in the early clearance of calcitonin and parathyroid hormone respectively. It is likely that the liver is the major site of the metabolism of calcitonin in vivo.
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SUMMARY
The metabolic clearance rate (MCR) of porcine calcitonin in six gilts was 13·0 ± 0·7 (s.e.m.) ml/min/kg and in four isolated, perfused pig livers was 16·1 ± 1·1 ml/min, with constant infusions of porcine calcitonin and measurement of calcitonin concentration by radioimmunoassay.
After single injections of 125I-labelled porcine calcitonin, the MCR of 125I-labelled porcine calcitonin was 29·2 ± 2·8 ml/min in six isolated, perfused pig livers.
125I-labelled salmon calcitonin was cleared at a slower rate than porcine calcitonin after single injections into the gilt. 125I-Labelled human calcitonin and 125I-labelled salmon calcitonin were not significantly cleared by the isolated, perfused pig liver.