The inhibitory effects of dopamine on adenohypophysial cells are mediated v
ia dopamine subtype 2 receptor (D2R). Dopamine agonists inhibit hormone rel
ease and induce tumor shrinkage in most prolactin-secreting adenomas, where
as in other adenoma types such effects are sporadic. We investigated D2R ge
ne expression by in situ hybridization (ISH) and immunocytochemistry in dif
ferent types of pituitary adenomas. By ISH, a variable D2R signal was detec
ted in 79 of 89 cases: 4 of 6 densely granulated and 8 of 8 sparsely granul
ated somatotroph, 4 of 4 mammosomatotroph, 7 of 7 mixed somatotroph-lactotr
oph, 4 of 4 acidophil stem cell, 16 of 16 sparsely granulated lactotroph, 1
1 of 16 corticotroph (functioning and silent), 3 of 4 silent subtype 3, 5 o
f 5 thyrotroph, 5 of 6 gonadotroph, 5 of 6 null cell, and 7 of 7 oncocytic
adenomas. By immunocytochemistry, D2R protein was localized in cytoplasm an
d nuclei of 60 of 62 adenomas. In lactotroph adenomas, long-acting bromocri
ptine (BECLAR) induced a major increase in D2R mRNA, which was not accompan
ied by increased D2R immunoreactivity, suggesting mRNA stabilization. In co
nclusion, D2R gene is expressed in the majority of pituitary adenomas repre
senting all tumor types. The significance of nuclear localization of D2R pr
otein remains to be clarified.