[Antitumor effect of bromocriptine on estrogen-induced rat prolactinomas: special reference to changes in secretory granules by stereological analysis].

Bromocriptine (CB) not only lowers serum prolactin (PRL) levels but also reduces tumor size of human prolactinomas. Gen et al and we have suggested that the size reduction of human prolactinomas by bromocriptine treatment results from the reduction in size of individual tumor cell as well as the reduction in number of tumor cells secondary to cell necrosis. This implies that bromocriptine has a cytosuppressive action and possibly a cytocidal action on human prolactinomas which causes reduction in cell size and cell necrosis, respectively. The mechanism of cytosuppressive action of CB has been investigated by using mostly non-neoplastic pituitary tissues of experimental animals. A decrease in exocytosis of secretory granules and a subsequent accumulation of granules within the cells are suggested to cause the reduction in serum levels of PRL in early stage of CB treatment. However we have reported that in spite of a pronounced reduction of serum PRL levels, the number of exocytosis of the granules in human prolactinomas treated with CB for 2 weeks increased to more than 4 times much as that in the untreated prolactinomas. This is a phenomenon which contradictory to the current hypothesis. The present study is intended to clarify whether the phenomenon we observed is specific for human prolactinomas or common also to the prolactinomas in experimental animals. Seventeen female SD rats were used. They were implanted subcutaneously with a pellet of 20 mg of 17 estradiol-benzoate (20% in cholesterol), and left to grow a pituitary tumor for 10 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)