Monoamine regulation of prolactin and TSH secretion in hypothyroidism

Dopaminergic and serotoninergic systems are involved in regulation of prolactin (PRL) and TSH secretion. About 10% of patients presented because of an galactorrhea and hyperprolactinemia (HP) have uncompensated primary hypothyroidism (PH). Two groups of patients were investigated using metoclopramide (MCP, DA antagonist, 10 mg i.v.), cyproheptadine (serotonin antagonist, 4 mg per os) and TRH tests. Group A consisted of 12 females with PH and hyperprolactinemia (HP). Group B presented 4 females with PH, HP and pituitary microadenoma on CT-scan. In control group of healthy euthyroid women basal PRL and TSH levels were in the normal range and statistically significant increase of both hormones was observed after MCP and TRH injections. Marked increase of basal TSH and PRL levels was found in both clinical groups. In contrast to control group no TSH reaction in MCP test was observed. PRL response to MCP was declined in group B versus group A. Cyproheptadine inhibited TSH secretion in patients with HP and PH, while this effect was absent in control group. TRH stimulated TSH and PRL response in group B was declined. Presented data shows that HP in PH may be due to the presence of subclinical microadenoma made manifest by hypothyroid state and/or due to disturbances in monamine control of PRL and TSH secretion.