Nucleic acid labeling with [3H]orotic acid and nucleotide profile in rats in protein deprivation, enteral and parenteral essential amino acid administration, and 5-fluorouracil treatment

Incorporation of 5-fluorouracil into hepatoma and normal tissue RNA at protein depletion in the rat

BACKGROUND AND OBJECTIVES

5-fluorouracil (5-FU) exerts its effects mainly by its incorporation into RNA and inhibition of DNA synthesis. Its toxicity may therefore be estimated by measuring its incorporation into RNA. Protein malnutrition has been considered to increase the toxicity of 5-FU.

METHODS

Rats with a hepatoma implanted into the liver were fed on either a 25% or a 0% casein diet for 1 week. On the last day, they were infused via the hepatic artery with a therapeutic dose of 3H-5-FU. Its incorporation into RNA was measured in hepatoma and several normal tissues.

RESULTS

Protein deprivation increased the incorporation of 5-FU into liver and intestinal RNA. Incorporation into hepatoma RNA did not increase significantly, but the ratio, liver/hepatoma RNA incorporation, remained unchanged.

CONCLUSIONS

Protein deprivation might increase the toxicity of 5-FU on liver and intestine.

Parenteral vs enteral nutrition in tumor-bearing rats

The development of cachexia may complicate cancer therapy, yet controversy exists concerning its nutritional management. For example, use of total parenteral nutrition (TPN) may not be appropriate because of gut atrophy, possible stimulation of tumor growth, and lack of total host protein repletion. In the present experiment, host and tumor responses were compared after identical parenteral or enteral nutritional supplementation (EN). Eighteen days after subcutaneous inoculation of adult male Fischer-344 rats with fresh methylcholanthrene-induced sarcoma (tumor-bearing [TB] rats), catheters were placed into either the external jugular vein or the stomach. Four days later, rats were started on an 11-day course of either TPN or EN with a Freamine-III-based formula (amino acids = 6%, dextrose = 21.5%, lipid = 1.5%). When the rats were killed, there was no difference in tumor weight between the various TB groups. Carcass weight was increased significantly in both the TB-TPN and TB-EN groups, and there was an elevation in gastrocnemius protein content in both groups compared with the TB-rat food group. Small intestine protein was preserved in the TB-EN group to the level observed in the control-rat food animals. Total lipids in the liver were increased in both TB-TPN and TB-EN groups; however, the magnitude of the increase was less in the TB-EN animals. Neither treatment resulted in complete protein repletion of tumor-bearing rats. EN may be more appropriate than TPN in that gut mass is preserved. The maintenance of gut mucosa may prove to be beneficial in the treatment of the depleted, immunocompromised, and metabolically stressed host.

Relation between the incorporation of 5-fluorouracil into liver carcinoma and normal tissue RNA at hepatic arterial administration in the rat is altered by overnight starvation

The cytotoxicity of 5-FUra has been related to its incorporation into RNA. In a model of secondary liver cancer in the rat, the incorporation of 5-FUra into the acid-soluble fraction, RNA and DNA of several normal tissues and an adenocarcinoma of the colon transplanted to the liver was determined. A therapeutic labelled dose of the drug was infused via the hepatic artery for 2 hr and the rats killed 1 hr later. Half of the rats were starved overnight before treatment. The incorporation of 5-FUra into liver and intestinal RNA increased at starvation. It was unchanged in kidney and bone marrow. The incorporation into tumor RNA decreased insignificantly. The incorporation into tumor RNA was significantly higher than in hepatic, intestinal, and renal RNA at ad libitum feeding. This difference disappeared at overnight starvation.