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

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Abstract
Thyroparathyroid glands were removed from 8 day old baby rats and incubated in vitro for up to 8 h. Release of both PTH [parathyroid hormone] and CT [calcitonin] into medium were measured using immunoassays that measure rat CT and rat PTH. Release of CT and PTH in vitro were inversely related. At 1 mM Ca, PTH in medium increased progressively up to .apprx. 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 5- to 10-fold (up to 10-20 ng/ml). Secretion of both CT and PTH were inhibited by 10-3 M 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.