COLOCALIZATION OF PROLACTIN AND PROLIFERATING CELL NUCLEAR ANTIGEN INTHE ANTERIOR-PITUITARY DURING ESTROGEN-INDUCED PITUITARY-TUMORS

Chronic estrogen treatment induces prolactin (PRL)-secreting pituitary tumors in laboratory animals. To determine earlier events of tumorige nesis, we studied cell proliferation in the pituitary following 7-30 d ays of estrogen administration in Fischer 344 rats. Immunohistochemica l localization of proliferative cells by proliferating cell nuclear an tigen (PCNA) staining and lactotropes by PRL staining revealed that es trogen treatment caused a time-dependent increase in the number of pro liferative cells and lactotropes. Although the increase in lactotropic cell number paralleled the increase in PCNA-reactive cell number, onl y approximately 30% of lactotropes reacted simultaneously with the PCN A antibody. These results indicate that a subset population of lactotr opes proliferates under the influence of estrogen during tumorigenesis .