Alpha smooth muscle actin (α-SM actin) in normal human ovaries, in ovarian stromal hyperplasia and in ovarian neoplasms

An immunohistochemical investigation of alpha-smooth muscle actin (α-SM actin) using the monoclonal anti-α-SM-1 antibody was carried out in 15 normal ovaries, in three ovaries with stromal hyperplasia and in 27 neoplastic ovaries. In selected cases the pattern of actin isoforms was examined by means of 2 D-gel electrophoresis. In addition, the tissues were stained for vimentin and desmin. In normal ovaries α-SM actin was found in the inner cortex and in the theca externa. In ovarian stromal hyperplasia expression of α-SM actin was minimal or absent. In primary and metastatic epithelial tumors there was positive stromal staining for α-SM actin, especially in the vicinity of epithelial elements. This tended to be more widespread in malignant neoplasms. Thecomas did not express α-SM-actin and could thus be differentiated from leiomyomas which stained intensely for α-SM actin. Only focal stromal staining of α-SM actin was observed in granulosa and germ cell tumors. In all the tissues studied blood vessels were strongly positive for α-SM actin. Desmin, although present in the stroma of most of the specimens, was less abundant than α-SM actin. We concluded that α-SM actin is a component of the normal human ovary where it may contribute to the contractility of its stroma. Its absence in the normal outer cortex and theca interna, and in stromal hyperplasia and thecoma implies that sex hormones do not constitute a stimulus for α-SM actin production in the ovary. Among neoplasms it is most widely represented in the stroma of epithelial tumors in which it may reflect stromal stimulation mediated by neoplastic epithelium. © 1989 Springer-Verlag