Concurrent Secretion of Calcitonin and Parathyroid Hormone in Vitro from the Rat Thyroparathyroid Complex

Abstract

Thyroparathyroid glands were removed from 8-day-old baby rats and incubated in vitro for up to 8 hr. Release of both PTH and CT into medium were measured using immunoassays that measure rat CT and rat PTH. Results showed that release of CT and PTH in vitro were inversely related. At 1 mM Ca, PTH in medium increased progressively up to ∼5 ng/ml while CT was only 1-2 ng/ml. At 2.5 mM Ca, PTH was suppressed to low levels (<0.5 ng/ml) while CT increased five- to tenfold (up to 10-20 ng/ml). Secretion of both CT and PTH were inhibited by 10-3M iodoacetate; at 2.5 mM Ca, CT secretion was inhibited 75% and, at 1 mM Ca, PTH release was inhibited >90%. PTH and CT release were not altered by several other agents tested, including secretin, pentagastrin, 1,25-(OH)2D3 and 24,25-(OH)2D3.