Effects of Estrogen and/or Pituitary Graft on Nucleic Acid Synthesis of Carcinogen-Induced Mammary Tumors in Rats2

Effects of estrogen and/or prolactin on the synthetic activity of DNA and RNA in 7,12-dimethylbenz-[a]anthracene-induced mammary tumors of rats were studied. Serum prolactin level was determined by radioimmunoassay. Ovariectomy resulted in a decrease of 3H-thymidine incorporation into DNA and an increase in the ratio of 14C-uridine incorporation into RNA: 3H-thymidine into DNA (14C/3H ratio). These changes returned to the control levels, with an elevated serum prolactin level, by either injection of 1 µg estradiol benzoate (EB) or isografts of 2 pituitaries; the effect was more marked in the former treatment than in the latter. Daily injection of 40 µg EB decreased 3H-thymidine incorporation into DNA and increased the 14C/3H ratio. This decrease in 3H-thymidine incorporation was ameliorated, with further marked increase in serum prolactin level, by simultaneous isografts of 6 pituitaries. In nucleic acid synthesis, prolactin was of primary importance for the growth of carcinogen-induced mammary tumors, although the participation of estrogen in this process could not be ruled out.