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Studies on mRNA of the Livers of Rats Force-fed a Threonine-devoid or Complete Diet^1,2,

Department of Pathology, University of South Florida, College of Medicine, Tampa, Florida 33620

Using an experimental kwashiorkor-like model induced in young rats by force-feeding a purified diet devoid of threonine for 3 days, the livers were investigated for alterations in mRNA metabolism and compared with those of control animals force-fed a complete diet. Hepatic RNA was labeled by administering a short pulse of ¹⁴C-orotate. Hepatic mRNA of the experimental animals revealed increased labeling in comparison to control animals. Also, selective digestion of mRNA of hepatic polyribosomes by ribonuclease treatment revealed that more polyribosomal mRNA was present in the livers of experimental animals than in the livers of control animals. Pretreatment with actinomycin D to inhibit RNA synthesis 10 hours before killing animals that had been force-fed for 3 days the complete or threonine-devoid diet revealed that the shift of hepatic polyribosomes toward heavier aggregates and the enhanced hepatic protein synthesis normally observed in the experimental animals was abolished. These results indicate that hepatic RNA synthesis, especially mRNA synthesis, is involved and is essential for shifting hepatic polyribosomes toward heavier aggregation and for enhanced hepatic protein synthesis in rats force-fed a threonine-devoid diet.

KEY WORDS: • threonine deficiency • hepatic mRNA • hepatic polyribosomes

¹ Supported by U. S. Public Health Service Research Grants AM-05908 and AM-16530 from the National Institute of Arthritis and Metabolic Diseases.

² A preliminary report was presented at the IX International Congress of Nutrition in Mexico City, 1972, Abstracts of Short Communications, p. 5.

Manuscript received 12 November 1973.