Bromocriptine effects on cultured human prolactin-producing pituitary adenomas: in vitro ultrastructural, morphometric, and immunoelectron microscopic studies.

In an effort to better characterize the ultrastructural, morphometric, and immunocytochemical changes induced by 10(-8) M bromocriptine (BR), tumor cells from three surgically removed PRL-producing pituitary adenomas were cultured on an extracellular matrix in serum-free medium. In each instance, the treated cultures were compared to control cells at the end of 24 h and 16 days. PRL RIAs were performed on culture medium. A decrease in cell and nucleus surface area was found on day 16 in two cultures. This supports the well known shrinkage of BR-treated PRL-producing adenomas. BR induced no change in these parameters in the tumor from a third patient who was partly resistant to the drug. Changes in the secretory process were discernible as of day 1 in all three tumors, with a dramatic reduction of exocytosis and intracellular accumulation of PRL-immunoreactive granules. This induced delayed inhibition of protein synthesis, demonstrated by preembedding immunocytochemistry on day 16. These results, obtained for the first time in human PRL-producing adenomas, are informative as to the subcellular events subsequent to short term BR treatment and illustrate that secretory inhibition and tumor shrinkage are not necessarily linked.