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Experimental Protein and Energy Deficiencies in the Rat^{1, 2,}

Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

Young male rats (100–130 g) were fed diets of equal energy content containing 0.5, 1, 2, 3, 5, and 18% lactalbumin consumed either freely or in restricted amounts. The rats receiving low protein diets failed to grow and mature. Those consuming the 0.5 and 1% protein diets given freely developed the characteristic features of kwashiorkor including edema, while those receiving the diets in restricted amounts developed the characteristic features of marasmus. The rats fed low protein diets had low plasma levels of essential amino acids; however, the lysine level was well maintained. The plasma levels of nonessential amino acids, especially glycine, alanine, and aspartic and glutamic acids were raised in marasmic rats but were reduced in rats fed low protein diets ad libitum. Young and severely malnourished rats appeared to have limited ability to synthesize urea. Therefore, they excreted more ammonia and other nitrogenous substances such as ethanolamine, and when given an amino acid load, intermediary metabolites of the ingested amino acids. Rats fed low protein diets showed diminution of total liver DNA, RNA, and protein. In addition to the reduction of protein synthesis resulting from decreased cellular RNA, ribosomes from the livers of protein-deficient rats had reduced ability to synthesize proteins. This defect was associated with the detachment of the ribosomes from endoplasmic reticulum membrane and the elevation of the proportion of monosomes to polyribosomes. Malnutrition did not produce any change in the turnover rate of liver RNA. Protein deficiency caused significant depression of serum insulin, thyroxine, and corticosterone levels. The overall conclusion is that mammalian metabolism is well adapted to dietary intake and that this adaptation is achieved through dietary control of synthesis and release of key metabolic hormones.

KEY WORDS: • malnutrition • liver protein synthesis • RNA • hormones

¹ Submitted to the Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Mass., in partial fuifillment of the requirements for the Ph.D. degree (L. E. A.).

² Requests for reprints should be addressed to Joseph Edozien, Department of Nutrition. School of Public Health, University of North Carolina, Chapel Hill, N.C. 27514.

³ Present address: Veterans Administration Hospital, Cell Biology Section, San Francisco, Calif. 94121.

⁴ Present address: Department of Nutrition, School of Public Health, University of North Carolina, Chapel Hill, N.C. 27514.

Manuscript received 7 February 1972.