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Effect of Hypocalcemia on Hormonal Responses to Thyrotropin-Releasing Hormone

Medical and Research Services, Veterans Administration Wadstvorth Hospital Center and Department of Medicine, UCLA School of Medicine Los Angeles, California

The effects of chronic hypocalcemia on pituitary and thyroidal responses to TRH were studied in six euthyroid and three mildly hypothyroid subjects with surgical hypoparathyroidism orpseudohypoparathyroidism. In the euthyroid patients, increments in serum TSH, T₃, and T₄ were equal under hypocalcemic or nonnocalcemic conditions;however, a slightly but significantly lower basal serum T₃ during hypocalcemia in conjunction with unaltered basalserum T₄ and reverse T₃ levels suggests that hypocalcemia may alter peripheral metabolism of T₄ and/or T₃.

Hypothyroid subjects showed more variable responses to hypocalcemia; after restoration of normocalcemia, two patients demonstrated greater serum T₃ increments following TRH and lowerTSH levels, suggesting an impairment of thyroidal secretion by hypocalcemia, while the third showed no effect of hypocalcemia on TSH, T₃, or T₄ responses to TRH.

Hypocalcemia had no effect on prolactin responses to TRH in the combined group of euthyroid andhypothyroid patients.

Since only minor effects on basal or TRH stimulated hormone levels were seen in all patients, it is concluded that hypocalcemia rarely has clinically significant effects on pituitary secretion of TSH and prolactin and thyroidal release of T₄ and T₃.

Received August 25, 1976.

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