Thyrotropin-releasing hormone stimulation of thyrotropin secretion is suppressed by calcium ion antagonists that block transmembrane influx and intracellular mobilization of calcium ion in human subjects.

To evaluate whether extracellular and intracellular calcium ion may be involved in the regulation of TSH secretion in response to TRH in human subjects, the TSH blood level was determined in normal man before and after administration of two kinds of calcium ion antagonists, nifedipine that blocks transmembrane influx of calcium ion and nicorandil that inhibits mobilization of intracellular calcium ion. Administration of nifedipine and nicorandil significantly decreased the blood level of TSH stimulated by TRH, although calcium ion antagonists did not affect the basal level of TSH. The blood level of neither T4, T3, free T4, free T3, nor reverse T3 was altered by administration of calcium ion antagonists. The present study indicates that cytoplasmic calcium ion derived from the extracellular and intracellular sources plays a pivotal role in the controlling of TRH-stimulated TSH secretion in human subjects.