Effect of dopamine agonists on lactotroph adenomas of the human pituitary

Dopamine (DA) agonists cause reduction of blood prolactin level and tumor s hrinkage in most patients with lactotroph adenoma. Our aim was to investiga te the cellular mechanism of tumor shrinkage by determining mitotic, MIB-1, p27, and apoptotic indices, as well as microvessel density (MVD), surface microvessel density (SMD), ploidy, and other nuclear parameters. Surgically removed lactotroph adenomas were selected from 29 patients, of whom 19 wer e treated with oral bromocriptine (BEC), long-acting injectable BEC (BEC-LA R), or quinagolide and 10 were untreated. In treated adenomas mitotic and M IB-1 indices were lower, whereas the apoptotic indices were not significant ly higher compared to untreated adenomas. The decrease in MIB-1 labeling re ached significance in adenomas exposed to quinagolide (p < 0.05). Aside fro m the BEC-LAR treated group, wherein p27 expression was significantly reduc ed (p < 0.05), p27 expression did not differ significantly between the trea ted and untreated groups. MVD density was significantly lower in the treate d adenomas, whereas the decrease in SMD did not attain significance. The DN A ploidy and most other nuclear parameters did not differ significantly in the two groups. In conclusion, reduction of mitotic and MIB-1 indices indic ates that suppression of cell proliferation contributes to tumor shrinkage, whereas p27 protein expression and apoptosis play no major role in the ade noma involution. Further studies are required to explain the effect of DA a gonists on MVD and SMD.