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  • Author: T. E. T. WEST x
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T. E. T. WEST, J. L. H. O'RIORDAN and A. D. CARE

SUMMARY

The plasma clearance of calcitonin (TC) was studied by following the disappearance of radioactivity after intravenous injection of labelled TC, and the disappearance of bio-assayable activity after intravenous injection of unlabelled hormone. The turnover was shown to be rapid: two exponential components were involved with half times of 4–5 and 35–40 min. respectively. Similar values were obtained in experiments in which TC was infused to obtain raised, steady concentrations after which the disappearance of biologically active material was followed for up to 100 min. The normal concentration of TC in porcine peripheral plasma was calculated to be about 9 μu./ml.

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T. E. T. WEST, J. L. H. O'RIORDAN, D. H. COPP, R. F. L. BATES and A. D. CARE

SUMMARY

Hypocalcaemia was produced by i.v. infusion of EDTA into pigs from which the thyroid venous effluent could be quantitatively collected. Calcitonin in the effluent was measured by radioimmunoassay. Reduction of plasma calcium concentration rapidly suppressed the secretion of calcitonin. In contrast, as plasma calcium was raised slowly from hypocalcaemic levels by infusion of CaCl2, calcitonin secretion quickly returned and increased rapidly. The secretion rate observed when the plasma calcium concentration had been raised from hypocalcaemia to the initial normocalcaemic level was 3½–10 times greater than that observed during the normocalcaemia which pertained at the start of each experiment. A previous period of hypocalcaemia also produced an exaggerated response to a subsequent hypercalcaemic stimulus. It is suggested that the preconditioned response of calcitonin secretion increases the efficiency of the role of calcitonin in calcium homeostasis.