Growth of separated and recombined neonatal rat uterine luminal epithelium and stroma on extracellular matrix: effects of in vivo tamoxifen exposure.

We have developed a system for serum-free culture of separated uterine epithelium and stroma from 11-day-old rats recombined on extracellular matrix extracted from Englebreth-Holm-Swarm tumors. Epithelium grew and, after 2 days in culture, developed into luminal epithelial spheres (LES) surrounding a fluid-filled lumen. Individual LES cells maintained epithelial cell characteristics such as basally located nuclei, apical microvilli (oriented toward the lumen), lateral membranes with interdigitations and desmosomes, secretory Golgi complexes, and abundant mitochondria and rough endoplasmic reticulum. Secretory vesicles were ubiquitous throughout the luminal fluid. Addition of 17 beta-estradiol to the growth medium increased the number and longevity of the LES. Prior exposure of uteri to tamoxifen via s.c. injection in vivo on postnatal Days 1 to 5 reduced or completely inhibited formation of LES in vitro. These effects occurred regardless of whether the stromal or epithelial component of the recombinant tissue was exposed to tamoxifen. These data suggest a directive property of neonatal stroma in culture resulting in the formation of highly secretory spherical epithelial structures completely enclosing a lumen. LES formation is responsive to both estrogen (positive response) and antiestrogen (negative response).