Estron-induced hyperplasia and neoplasia in the rat anterior pituitary gland

Different doses of estron （El） were administered to 97 F344 and wistar rats. After 30, 45 and 60 days, the weight and histological change in the pituitary gland were observed. 24 rats were used as a control group. Prolonged administration of El resulted in weight increase and hyperplasia or neoplasia in the pituitary gland. The weight of pituitary gland was significantly increased than that in control rats（P＜0.01）. Histological study showed that 34% rats revealed neoplasia and 46.% revealed hyperplaia in pituitary glands, These changes were most significant during the period of 45 days after El administration. There was no significant difference in the incidence of neoplasia between two El dose groups. There was significant difference between F344 and Wistar rats with El evoking pituitary tumor. But, there was no significant difference between male and female rats and between ovariectomized rats and not ovariectomized rats. These data indicate that the El-induced pituitary adenoma may be a good model for human prolactinomas that might be utilized for study of the mechanism and treatment of pituitary ademoma.