Pathogenesis of blood-filled cavities in estrogen-induced anterior pituitary tumors in male Sprague-Dawley rats

The formation of blood-filled cavities in developing tumors of the anterior pituitary of estrogen-treated male Sprague-Dawley rats was studied in a serial sacrifice experiment. Two treated and 2 control rats were killed at each of 15 time points ranging from 7-272 days after sc implantation of an estradiol-17β pellet. The pituitaries were examined using light and electron microscopy. Changes at 7-9 days after implantation included epithelial cell swelling and trabecular arrangement. At 11-13 days, epithelial cells were further enlarged. Arrangement of epithelial cells in islands and endothelial degeneration were first seen at this interval. Also, any sinusoids were distended, whereas some were compressed by swollen epithelial cells. At 16-81 days, scattered necrotic and immature epithelial cells were present, and cell size decreased. Endothelial degeneration and both distended as well as compressed sinusoids were more prominent at this time. Loss of basement membrane was first seen during this interval. A...