Effect of 5-Fluorouracil in Pregnant Rats Bearing Walker Carcinosarcoma 256

5-Fluorouracil was adiministered by endoperitoneal route at a daily dose of 10 mg/kg to pregnant female rats and to pregnant rats bearing Walker's carcinoma 256. In non-tumor-bearing animals it induced a marked reduction in the number and mean weight of living new-borns per delivery, while foetuses from tumor-bearing pregnant rats showed number and weight only slightly lower than normal. Tumor development was markedly inhibited both in pregnant and in non pregnant animals. Foetuses from tumor bearing rats showed an increase in nucleic acids and a reduction in the hepatic glycogen, while in foetuses from tumor bearing rats treated with 5-fluorouracil a marked fall was observed both in nucleic acids and in hepatic glycogen. In the blood of foetuses from tumor bearing rats a 20 percent reduction in glucose was observed, while 5-fluorouracil treatment determined a slight glucose diminution and a market increase of ureic concentration. The obtained results suggest trat the antimetabolite, inducing serious alterations in foetuses from treated rats, is much less active when there is a transplanted tumor (Walker's carcinoma 256) in the maternal organism. Probably this is due to the competitive-type action exerted by the highly proliferating tumor tissue on the embryonal tissue, in respect of 5-fluorouracil. The difference in intensity of effect on tumor and on foetus is mainly due to the fact that the tumor, owing to the « re-ciclization » phenomenon, retains fluorouracil prolonging its action, while the foetus eliminates it by means of the normal purinic and pyrimidinic metabolism of nucleic acids.