Bromocriptine treatment reduces the cell size in human macroprolactinomas: a morphometric study.

A morphological study was carried out on eight macroprolactinomas surgically removed from untreated patients and on nine macroprolactinomas removed from patients treated with bromocriptine (Brc; seven from patients treated for 6 weeks and two from patients treated for 1 yr). All treated patients had both serum PRL levels and tumor size (by computed tomographic scan) reduced. The study was carried out using light, immunofluorescence, and electron microscopic techniques and electron microscopic morphometry. By immunofluorescence microscopy, all tumors consisted of cells positive for PRL. In some treated tumors, the fluorescence was more marked than in untreated tumors. By light and electron microscopy and by morphometry, significant reductions in cell size were observed in the adenomas from Brc-treated patients. Both the cytoplasm and the nucleus shrank, but the reduction of the cytoplasm was much greater than that of the nucleus. The shrinkage of the cytoplasm was a consequence of marked involution of the rough endoplasmic reticulum and the Golgi complex in Brc-treated tumors. This effect may be related to inhibition of PRL synthesis by the drug. In some tumors from treated patients, the number of secretory granules was increased. No differences were observed between tumors from patients treated for 6 weeks and those from patients treated for 1 yr. The observed reduction in cell size by Brc could explain, at least in part, the well known size reduction of PRL-secreting adenomas in patients treated with the drug.