Thyroid Hormone Inhibition of the Prolactin Response to Thyrotropin—releasing Hormone

Abstract

influence of serum triiodothvronine (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 A prolactin) was used as the index of response to TRH. In 12 patients with primary hypothyroidism, the maximum A 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 Nk of treatment with 30 jug T3 + 120 jug T4 daily. The mean serum T3 level increased from 57±8 to 138+10 ngl100 nml! and the mean serum T4 level increased from 3.0±0.4 to 7.2±0.4 Ag/lOO ml during this treatment. In eight normal subjects the maximum Aprolactin in response to TRH was not significantly different during the 4th wk of treatment with 30 Ag T3 + 120 /g T4 daily from the response before treatment. In 10 patients with hvperthyroidism, the maximum Aprolactin in response to TRH increased from 14.2±2.9 ng/ml before treatment to 46.9±6.7 nig/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 Ig/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,

Prolactin and Male Reproduction

“…testosterone level. An altered secretion of PRL, despite a normal basal level, might be responsible for clinical symptoms such as impotence and oligozoospermia, and for testosterone modification that can be demonstrated by an abnormal PRL response to TRH [203]. Even after careful examination, however, the differential diagnosis is complicated by the fact that some cases classified as functional because of a normal pituitary fossa at neuroradiological studies may have a micro-adenoma that escapes diagnosis.…”

Persistent Hemichorea Associated with Thyrotoxicosis.

“…Since the concentration of homovanilic acid is decreased in the cerebrospinal fluid in hyperthyroidism (17), the pro duction and turnover of dopamine by negative feedback may be decreased. Some investigators (18)(19) reported a diminished prolactin response to TRH in hyperthyroid ism, suggesting enhanced central dopaminergic tone.…”

14. Approach to the Patient with Persistent Hyperprolactinemia and Negative Sellar Imaging

“…The major mechanism causing hyperprolactinemia in primary hypothyroidism is an increase in the levels of TRH, which stimulates PRL secretion (9).…”