A Bioassay for Parathyroid Hormone Based on Hormonal Inhibition of CO2Production from Citrate in Mouse Calvarium

Abstract

An in vitro method has been developed as bioassay for parathyroid hormone. It is based on the inhibition by the hormone of ¹⁴CO₂ yield produced by the metabolism of ¹⁴C-citric acid in mouse calvarial organ culture system. The log-dose response plot was linear over the range of 0.0025 to 0.15 μ/ml. The method is capable of detecting parathyroid hormone when net bone resorption (calcium release to the medium) is inhibited by removal of serum from the culture medium or by addition to the system of thyrocalcitonin, or high concentrations of phosphate. Moreover, the response of the system to parathyroid hormone was essentially unaffected by a wide range of calcium in the culture medium. Inactive components in crude parathyroid hormone preparations were inactive in this system as was peroxide-inactivated parathyroid hormone. The response of the system is related to events associated with bone resorption, since agents such as dibutyryl cyclic AMP, 25-hydroxycholecalciferol, vitamin A and heparin which are effective in this process, also produced an inhibition of ¹⁴CO₂ yield. (Endocrinology89: 1425, 1971)