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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.

Hypercalcaemic perfusion of such a parathyroid gland usually resulted in a prompt systemic hypocalcaemic response but it was impossible to conclude with certainty that this was not merely due to the cessation of parathyroid hormone secretion. Although no effect was observed in acute experiments, cross-transfusion of parathyroid venous plasma during hypercalcaemic perfusion of the gland in conscious sheep was followed by a small hypocalcaemic response in the two 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 hypocalcaemia, followed later by hypercalcaemia.

In general, similar changes in plasma magnesium concentration accompanied those of plasma calcium concentration as a result of hypercalcaemic 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 hypercalcaemia, although the possibility cannot be entirely eliminated.

This article has been cited by other articles:

				M. A. Aliapoulios, D. S. Bernstein, and M. C. Balodimos Thyrocalcitonin: Its Role in Calcium Homeostasis Arch Intern Med, January 1, 1969; 123(1): 88 - 94. [Abstract] [PDF]