Dopamine D2 receptor gene expression in human adenohypophysial adenomas

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.