Influence of Hormone-Secreting Pituitary Tumors on RNA Biosynthesis in Rat Anterior Pituitary

Summary

The hypothesis that pituitary tumor implants cause atrophy of the host's pituitary gland by altering RNA metabolism of the gland was investigated. Pituitary glands were incubated 4 hours with ³H-uridine or ³H-guanosine; the RNAfrom glands of normal and tumor-bearing animals produced similar sucrose-gradient profiles, with 3 peaks corresponding to about 28S, 18S, and tRNA. However, the glands of animals with prolactin- and growth hormone-secreting tumors, MtTW5 and MtTW15, consistently yielded less RNAthan did control glands. The specific activity of the RNA, however, was significantly higher than that of control RNA. Estradiol treatment of the animals increased the amount of RNA in both control glands and those of tumor-bearing animals. At the same time, in vitro incorporation of ³H-uridine was decreased; this resulted in less specific activity in the glands of tumorbearing animals. When glands were preincubated with ³H-uridine and the labeled compounds “chased” with excess unlabeled uridine and actinomycin D, pituitary RNA of turrior animals had a higher turnover rate than control RNA. This observation, along with the decreased amount of RNA in the tumor animal gland, may explain the reduction in prolactin and growth hormone synthesis.