Classical experiments1-3 have suggested and more recent studies 4,5 by radioimmunoassay have confirmed that the secretion of parathyroid hormone (PTH) is controlled by the serum calcium. There is a proportional relationship between hormone secretion in vivo and the serum calcium with rapid changes in the circulating level of PTH being noted within minutes after alterations in extracellular ion concentration.6 Hypermagnesemia will also suppress the release of hormone from the parathyroid glands.5
Exception to such tightly controlled homeostatic regulation may be found in patients with primary hyperparathyroidism due to a parathyroid adenoma or diffuse hyperplasia. Chronic hypocalcemia of even mild degree will produce significant secondary hyperplasia of the parathyroid glands, which may occasionally become autonomous ("tertiary" hyperparathyroidism) in long-standing stimulation.7-9 The development of autonomous hyperparathyroidism is suggested by the appearance of hypercalcemia during chronic renal disease or after transplantation of the kidneys and correction of renal
Sherwood LM, Herrmann I, Bassett CA. In Vitro Studies of Normal and Abnormal Parathyroid Tissue. Arch Intern Med. 1969;124(4):426–430. doi:10.1001/archinte.1969.00300200038007
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