Calcitonin release from medullary thyroid carcinoma by thyrotropin-releasing hormone: comparison with calcium injection

Abstract

The effects of thyrotropin-releasing hormone on the release of calcitonin were investigated in 15 normal subjects and 12 patients with medullary thyroid carcinoma. The present study also compared the effect of TRH stimulation with calcium infusion test on calcitonin release in patients with medullary thyroid carcinoma. In normal subjects, calcitonin increased from a basal value of 7.5±2.5 pmol/l to a peak value of 9.4±3.0 pmol/l (p<0.01) after iv injection of synthetic TRH (500 μg). Basal calcitonin values in patients with medullary thyroid carcinoma were high (1216±2230 pmol/l, p<0.05), and TRH induced a further increase in calcitonin to 1 842±3149 pmol/l in all the patients (p< 0.05). They had a peak value of 7891±13 528 pmol/l after the calcium infusion, which was significantly higher than the basal value of 1463±2630 pmol/l (p<0.05). All medullary thyroid carcinoma patients displayed a marked calcitonin increase after TRH and calcium stimulation. Although the increase in serum calcitonin after TRH injection was lower than that after calcium injection (1.6-fold vs 5.4-fold, p <0.05), there was no significant difference in mean peak calcitonin value following TRH and calcium injection in patients with medullary thyroid carcinoma. These results indicated that TRH could stimulate calcitonin release from the thyroid C-cells in both normal subjects and patients with medullary thyroid carcinoma.