Effects of bromocriptine on prolactin-secreting pituitary adenomas. Mechanism of reduction in tumor size evaluated by light and electron microscopic, immunohistochemical, and morphometric analysis.

Prolactin-secreting pituitary adenomas were studied to clarify the mechanism by which bromocriptine reduces tumor size. Patients examined consisted of three groups: Group I (four cases) received no medication, Group II (six cases) continued bromocriptine treatment (10 mg/day for 2 weeks) until the operation, and Group III (five cases) discontinued the treatment 1 week before the operation. Adenomas in Group II showed a variety of degenerative and necrotic changes of tumor cells in addition to marked decrease in volume of individual cell. Adenomas in Group III showed divergent structural changes. Irreversible changes seen in Group II became more pronounced with a marked increase in stromal tissue. Proliferative areas consisting of intermediate-sized cells were found in the scarce stromal tissue. The findings seem to indicate that the reduction in size of prolactinomas by bromocriptine treatment results from the reduction in size of individual tumor cell as well as from cell loss secondary to necrosis.