THYROTROPHIN RELEASING HORMONE INDUCED CALCITONIN SECRETION IN PATIENTS WITH MEDULLARY CARCINOMA OF THE THYROID

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Abstract
An i.v. bolus injection of 500 .mu.g TRH caused a prompt increase in plasma calcitonin (CT) in two patients with medullary thyroid carcinoma (MTC). In case 1 with a sporadic MTC, plasma CT increased from 0.32 ng/ml to 0.70 ng/ml 2 min after TRH. In the second case with multiple endocrine neoplasia (MEN) type II, plasma CT increased from 0.39 ng/ml to 4.7 ng/ml 2 min after the injection. None of five normal healthy subjects and a patient with thyroid follicular adenocarcinoma had significant changes in plasma CT levels after TRH. Studies with monolayer cultures of MTC cells derived from one patient revealed that TRH stimulated CT release. Incubation of the cells with TRH of 10-6 M or 10-5 M for 1 h increased CT concentration in the medium to 140% or 182% of the control level, respectively. Under the same conditions, pentagastrin (10-6 M) increased CT concentration in the medium to 156%. These results indicate the direct stimulatory effect of TRH on CT secretion in the patients with MTC.