Interaction of retinoic acid and 3-methylcholanthrene on the fine structure of mouse prostate epithelium in vitro.

The effects of 3-methylcholanthrene (MCA) and retinoic acid (RA) on the fine structure of AKR mouse prostate epithelium in organ culture were correlated with changes in cell proliferation. In intact glands before explantation, the epithelial cytoplasm showed concentric flat or globular cisternae of endoplasmic reticulum in both supranuclear and basal areas, a well-developed Golgi complex, secretory vesicles, and numerous microvilli at the luminal surface. After explantation, the cytoplasmic organelles, particularly the endoplasmic reticulum, regressed and tonofilaments appeared. The regression was largely prevented by RA. MCA induced considerable epithelial hyperplasia and squamous metaplasia. The fine structure of the newly formed cells revealed a complete loss of endoplasmic reticulum, Golgi apparatus, secretory vesicles, and microvilli, with the appearance of bundles of tonofilaments and a striking increase in the number of desmosomes. Administration of RA to explants pretreated with the carcinogen partially reversed the hyperplasia and squamous metaplasia. The tonofilaments disappeared and the number of desmosomes greatly decreased, whereas endoplasmic reticulum, Golgi complex, secretory vesicles, and microvilli were largely reestablished. Planimetric measurements of the alveolar epithelium showed that the squamous transformation and its partial reversal by RA coincide with the rise and decline of epithelial hyperplasia. The data suggest that the restoration of secretory differentiation by RA was responsible for the initial breakdown of the hyperplastic epithelium, whereas the lowering of DNA synthesis by RA prevented further hyperplasia and kept cell replication within normal limits.