The effect of nomifensine on thyroid-stimulating hormone (TSH) in normal and hyperprolactinemic subjects

Thyroid-stimulating-hormone (TSH) secretion was studied in 28 normal subjects (12 males; 16 females) and in 8 subjects with prolactin (PRL) secreting tumors (1 male; 7 females) after nomifensine (NOM) administration (200 mg orally). NOM is a drug which activates dopaminergic (DA) neurotransmission at the central nervous system level. Blood samples were drawn every hour for 4 h after NOM or placebo administration. On the 4th h thyrotrophin-releasing-hormone (TRH) was administered in bolus (200 micrograms i.v.), to both groups, and additional samples were collected at 10-, 20-, 30-, 60- and 90-min intervals. The results indicate that in normal subjects, but not in prolactinomas, NOM induces a moderate but significant reduction in TDH secretion. Furthermore, the TSH response to TRH was found to be significantly reduced. No variation was discerned, however, in PRL secretion after NOM. The hormone response to TRH remained unaffected. The data confirm that in normal subjects the DA neurotransmission exerts an inhibitory role upon TSH secretion. In subjects affected by prolactinomas, an alteration in central DA availability may be hypothesized.