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-17 beta 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. At 114-133 days, small hemorrhagic areas partially lined by epithelium were first seen; sinusoidal compression, endothelial necrosis, and loss of basement membrane were more frequent, but there was less sinusoidal distention. Between 150 and 272 days, epithelial cells were increasingly pleomorphic and arranged in nodules, and there was an increase in number and size of the hemorrhagic areas. Sinusoidal compression, endothelial necrosis, and loss of basement membrane were abundant, whereas sinusoidal distention had almost disappeared at this interval. Local compression of sinusoids and perhaps compression of pituitary surface veins due to epithelial cell swelling, were thought to play a primary role in the development of ischemic endothelial damage leading to loss of endothelial lining and basement membrane, and eventually to the formation of blood-filled spaces partially lined by epithelial cells.