Thyroid Hormone Inhibition of the Prolactin Response to Thyrotropin-Releasing Hormone

Peter J. Snyder; Laurence S. Jacobs; Robert D. Utiger; William H. Daughaday

doi:10.1172/JCI107421

Thyroid Hormone Inhibition of the Prolactin Response to Thyrotropin-Releasing Hormone

Peter J. Snyder, Laurence S. Jacobs, Robert D. Utiger, and William H. Daughaday

Published September 1, 1973 - More info

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Abstract

The influence of serum triiodothyronine (T₃) and thyroxine (T₄) concentrations on the release of prolactin in man was studied by determining the prolactin response to synthetic thyrotropin-releasing hormone (TRH) in hypothyroid and hyperthyroid patients before and after correction of their serum thyroid hormone abnormalities. The maximum increment in serum prolactin above the basal level (maximum Δ prolactin) was used as the index of response to TRH.

In 12 patients with primary hypothyroidism, the maximum Δ prolactin in response to TRH fell from 100.5±29.1 ng/ml (mean ±SEM) before treatment to 36.1±6.0 ng/ml (P < 0.01) during the 4th wk of treatment with 30 μg T₃ + 120 μg T₄ daily. The mean serum T₃ level increased from 57±8 to 138±10 ng/100 ml, and the mean serum T₄ level increased from 3.0±0.4 to 7.2±0.4 μg/100 ml during this treatment. In eight normal subjects the maximum Δprolactin in response to TRH was not significantly different during the 4th wk of treatment with 30 μg T₃ + 120 μg T₄ daily from the response before treatment. In 10 patients with hyperthyroidism, the maximum Δprolactin in response to TRH increased from 14.2±2.9 ng/ml before treatment to 46.9±6.7 ng/ml (P < 0.001) during antithyroid treatment. The mean serum T₃ level fell from 313±47 to 90±8 ng/100 ml, and the mean serum T₄ level fell from 20.8±2.5 to 6.8±0.6 μg/100 ml during this treatment.

These results show that changes from normal serum levels of T₃ and T₄ are associated with changes in prolactin responses to TRH; subnormal serum levels of T₃ and T₄ increase TRH-induced prolactin release, whereas substantially higher than normal serum levels of T₃ and T₄ inhibit this release.