Biochemical and ultrastructural studies on estrogen-induced pituitary tumors in F344 rats

The hormone function, the metabolism of nucleic acids, and the ultrastructure of estrogen-induced pituitary tumors and of normal glands were examined in male F344 rats. The tumors had a high capacity for prolactin (PRL) synthesis, and the plasma levels of PRL were elevated 65-fold to 100-fold in the tumor-bearing animals. Uridine uptake and phosphorylation to nucleotides, as well as uridine incorporation into total RNA, were similar in tumors and normal glands, whereas [3H]thymidine incorporation into DNA was double in the former group as compared to the latter. After a [3H]uridine pulse, labeled RNA turnover was different in tumors and normal glands. Electron microscopy of the tumors revealed hypertrophy, degranulation, and hyperplasia of cells producing PRL with proliferation of their ergastoplasm in whorls. Other pituitary cell types were reduced in number. It is suggested that the whorl configuration caused the high rate of protein and PRL synthesis as well as the changes in RNA metabolism displayed by the tumors.