Although dopamine receptors have been found on human pituitary adenoma cells, it is not certain if they are functionally intact. Receptor sensitivity to dopamine may be diminished, which would explain the lack of response to increased endogenous dopamine stimulation; however, the obvious response of the receptors to pharmacologic dopamine agonists makes this possibility less likely. Certain drugs act as dopamine receptor-blocking agents, including phenothiazines (e.g. chlorpromazine), butyrophenones (haloperidol), and benzamides (metoclopramide, sulpiride, and domperidone). These drugs block the effects of endogenous dopamine and thus release lactotrophs from their hypothalamic inhibition. This sequence of events results in hyperprolactinaemia.
