Thyroid and Parathyroid Roles in Hypercalcemia: Evidence for a Thyrocalcitonin-Releasing Factor.

Extirpation of either the parathyroids or the thyroid in rats acutely impaired their ability to counteract hypercalcemia induced by exogenous parathormone. Thyroidectomy had the greater effect, and in rats subjected to both parathyroidectomy and thyroidectomy the calcium-lowering mechanism was not further impaired, which suggests that the parathyroids secrete a humoral factor that releases calcium-lowering thyrocalcitonin from the thyroid. This hypothesis reconciles previous conflicting reports.