Early response of vaginal epithelium to benzo[a]pyrene in ovariectomized rat: morphological and cytochemical studies

Bilaterally ovariectomized rats (Sprague-Dawley) were used to study the early effects of benzo(a)pyrene (BP) on the morphology and cytochemistry of vaginal epithelium. BP (50 mg/kg) was administered subcutaneously in 0.5 ml corn oil and dosing was daily for 2--6 days. Animals were sacrificed 24 hr after the last dose; and vaginal tissue was processed separately for light and electron microscopy, and ultracytochemistry. The results indicate that BP alone induces mucification, mitosis and DNA synthesis in the superificial and basal comportmanets of vaginal epithelium, and DNA synthesis in the submucosal layer. BP also enhances alkaline phosphatase activity and glycogenesis. Alkaline phosphatase is present in the plasma membranes of various cells and in the membranes delimiting secretory granules. Increased alkaline phosphatase is associated with cell growth and proliferation, and also with mucin formation and secretion. Glycogen is relatively abundant in the intermediate cells and parabasal cells. Further, periodic acid-silver methenamine staining indicates that secretory granules and mucin contain glycoproteins. An examination of the fine structure of mucocytes reveals that Golgi complex and granular endoplasmic reticulum are involved in the fabrication of mucin which is secreted by apocrinal and exocytotic processes. Increased mucification was observed after two days (2 doses) and intensified up to 6 days (6 doses). These findings provide evidence that BP is mucinogenic and mitogenic agent to vaginal epithelium in spayed rats without the presence of exogenous ovarian hormone promoting or inducing factors.