Expression of dopamine 2 receptor subtype mRNA in clinically nonfunctioning pituitary adenomas

Dopamine receptor agonists (DAs) can reduce hormone release and tumor mass in the majority of prolactinomas, whereas such effects are controversial in clinically nonfunctioning pituitary adenomas (NFPAs). Whether expression of dopamine 2 receptor (D2R) is different in subgroups of NFPAs has not been fully elucidated. We assessed and compared D2R subtype (long: D2L and short: D2S) mRNA levels in subgroups of NFPAs by real-time reverse transcriptase polymerase chain reaction (RT-PCR). For both D2L and D2S mRNA, there were no significant differences among them. Only 21.6% of NFPAs showed relatively high D2R mRNA levels; furthermore, histopathological subtypes of those cases with relatively high D2R expression were gonadotropinomas and null-cell adenomas. These data suggest that DAs are effective only for a small proportion of NFPAs, and relatively high D2R expression may more possibly happen to a subset of gonadotropinomas and null-cell adenomas.