Effect of Hypocalcemia on Hormonal Responses to Thyrotropin-Releasing Hormone

Abstract

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 on...