Abstract： Objective The aim of this study is to analyze the ultrastructural changes and dopamine 2 receptor(D2R) expression levels of pituitary adenomas to clarify the mechanism of medical management.Method 9patients with prolactinomas and 4 with nonfunctioning pituitary adenomas( NFPAs)were treated with bromocriptine preoperatively.Ultrastructure changes of tumor cells were observed through electron microscopy.Tumor tissue samples were examined for the expression of both ER mRNA and D2R mRNA isoforms by means of QRT- PCR analysis.Results Expressions of D2S mRNA、 D2L mRNA、 ERα mRNA were significant difference between prolactinomas and NFPAs( P ＜0.01, P ＜0.01, P =0.019,respectively),in which was higher in prolac tinomas as compared to NFPAs.Except for 1 patient with densely granulated lact otroph adenomas,8 sparsely granulated lactotroph adenomas showed that cytoplasm was shrunken and the karyoplasmic ratio was enlarged.Ultrastructural analysis confirmed a series of changes including nuclear chromatin aggregation and margination,marked reduction of rough endoplasmic reticulum and Golgi complexes, vascular degenerations, necrosis and autolysis of tumor cells with dark cell or naked nuclear cell Compared to prolactinomas,NFPAs had little changes in cell size and cytoplasmic apparatus but also had chromatin aggregation, cytoplasmic vacuolization and unconspicuous necrosis of tumor cell.Conclusions This study shows the differential expression of ER mRNA and D2R mRNA isoforms between prolactinomas and NFPAs.Comparinb to prolactinomas,NFPAs with medical treatment also have some ultrastructural changes according to their exression levels of D2R isoforms.Ultrastructural changes in those adenomas are closely correlated with the expression levels of D2R isoforms.