AN INVESTIGATION INTO THE PARATHYROID ORIGIN OF CALCITONIN

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Abstract
To investigate the part played by the parathyroids as a source of calcitonin under controlled conditions, conscious, thyroidectomized animals have been used, in which a superior parathyroid was perfused with blood of variable composition and parathyroid venous blood could be collected at will. Hypercalemic perfusion of such a parathyroid gland usually resulted in a prompt systemic hypo-calemic response but it was impossible to conclude with certainly that this was not merely due to the cessation of parathyroid hormone secretion. Although no effect was observed in actue experiments, cross-transfusion of parathyroid venous plasma during hypercalcemic per-fusion of the gland in conscious sheep was followed by a small hypo-calemic response in the 2 recipient lambs. The time-course of this response was similar to that obtained in sheep following the intravenous injection of extracts of bovine superior parathyroid glands. However, pure parathyroid hormone, injected intravenously into a sheep, was also found to cause an initial hypocalcemia, followed later by hypercalcemia. In general, similar changes in plasma magnesium concentration accom -panied those of plasma calcium concentration as a result of hypercalemic perfusion of a parathyroid gland or the intravenous injection of bovine parathyroid extracts. It is impossible to conclude with certainty that, in the sheep, the parathyroid glands secrete calcitonin in response to the stimulus of hypercalcemia, although the possibility cannot be entirely eliminated.

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