Structural changes in human pituitary tumor after bromocriptine therapy.

The histological appearance of a prolactin-producing tumor and of a growth hormone-producing tumor after short term bromocriptine therapy was studied in detail using light microscopy with conventional and immunocytochemical methods and using transmission electron microscopy. The findings were correlated with clinical, radiological, and biochemical data. Histological changes consisting of clumping of nuclear chromatin and a marked reduction in cytoplasmic volume due to loss of ribosomes, rough endoplasmic reticulum, and Golgi complexes were observed only in the prolactin-producing tumor. Normalization of elevated serum prolactin levels and reduction in size of the tumor observed in serial computed tomograms correlated with striking histological changes found in the tumor. These changes were interpreted to represent a reversible inhibition of the protein-synthetic machinery of the neoplastic cell. Comparable clinical, biochemical, radiological, or structural changes were not observed in the growth hormone-secreting tumor.