Immunodetection of chorionic gonadotropin and its subunits in human nonfunctioning pituitary adenomas

Human nonfunctioning pituitary adenomas (NFPA) may produce CG in addition to the classical glycoprotein hormones (LH, FSH, and TSH). The aim of the present study was to localize LHβ, FSHβ, TSHβ, α-subunit (αSU), CG, and its β-subunit (βSU) in NFPA using a highly specific immunohistochemical technique. Nine NFPA, obtained at surgery, were processed for both electron microscopy and immunohistochemistry. Three tumors resulted oncocytomas, and six were null cell. Using an immunofluorescence technique, all tumors were positive for at least one glycoprotein; in particular, seven adenomas were markedly positive for CGβ, whereas only two were positive for the intact CG. No association among LHβ, FSHβ, and CGβ positivity could be demonstrated in the different adenomas. In the seven tumors positive for both CGβ and αSU, double fluorescence labeling demonstrated that six cases localized CGβ and αSU in different cells, but only one tumor showed the two subunits colocalized in the same cells. These data confirm that pituitary tumors synthesize both αSU and βSU of glycoprotein hormones; in particular, the present study indicates that the majority of NFPA is able to synthesize CG, particularly its βSU. Moreover, the localization of CGβ and αSU in different tumoral cells might account for the preferential expression of βSU and αSU instead of the intact hormonal molecules in NFPA.