Lack of Direct Effects of Calcitonin and Parathyroid Hormone on in Vitro Secretion of One Another from Rat Thyroparathyroid Glands 1 2

Abstract

Summary

Thyroid and parathyroid glands from 8-day-old rat pups were incubated both separately and together for 8 hr in a serum-free medium. In addition, thyroparathyroid complexes were incubated in the presence or absence of added bovine PTH or rat or salmon CT. Secretion of PTH and CT was measured using radioimmunoassays that detect rat PTH and rat CT. In all experiments, secretion of CT was 5- to 10-fold greater in 2.5 mM Ca than in 1 mM Ca. Conversely, PTH release was 5- to 10-fold higher in 1 mM Ca than in 2.5 mM Ca. PTH secretion was no different whether the thyroid gland was present with the parathyroids or not, and CT release from thyroids was not affected by the presence or absence of the parathyroid glands. The results support the conclusion that the thyroid gland (CT) exerts no direct influence on the ability of the parathyroids to release PTH and that the parathyroid (PTH) exerts no direct effect on the release of CT from the thyroid gland.