Ultrastructural study of cultured smooth muscle cells from uterine leiomyoma and myometrium under the influence of sex steroids.

Upon the hypothesis that the differentiation or development of smooth muscle cells in both myometrium and leiomyomas may be under the regulation of sex steroids, myometrial and myoma cells were cultured in the presence of sex steroids and their morphological changes were studied ultrastructurally. The cells from the explants of both leiomyoma and myometrium at the 14th day in either control or E (10(-8) M 17-beta-estradiol)-added medium showed extremely well-developed cytoplasmic organelles with few filaments located at the marginal portion of the cytoplasm. These ultrastructural features resembled those of a dedifferentiated stage of smooth muscle cells in vitro. At the 21st day, these cells showed a moderate number of cytoplasmic filaments with dense bodies. These ultrastructural features resembled those of a redifferentiated stage of smooth muscle cells in vitro. In both E- and P (10(-7) M progesterone)-added medium, the cultured smooth muscle cells from both leiomyoma and myometrium showed an increased number of myofilaments with dense bodies even at the 14th day to the 21st day of culture in comparison to the cells either in control or estrogen-added medium. Therefore, the cultured smooth muscle cells in the medium with E and P lacked their dedifferentiated phase in vitro and/or the differentiation or maintenance of their filaments might be under the influence of both estrogen and progesterone. On the observation that the cultured smooth muscle cells from both leiomyoma and myometrium showed very similar ultrastructural changes under the influence of sex steroids, it was suggested that leiomyoma may have the same progenitor cells as myometrium.