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Effects of Energy or Protein Deprivation and Subsequent Rehabilitation on Protein and DNA Content of Several Organs in Rat Pups

Department of Human Nutrition and Foods, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061

The separate effects of protein and energy restriction, and subsequent rehabilitation during the early period of life on cellular development in rats were studied. New born male pups were randomly assigned to foster dams in litters of eight. Foster dams were restricted to about 10 g of feed a day during the first 10 days of lactation, and 20 g of food a day for the remainder of the study. Litters were divided into basal, low protein and low energy groups. Rat pups were supplemented with either a basal, low protein or a low energy diet 12 times daily for 10 and 20 days. Organ DNA and protein were determined in brain, thymus, heart, lungs, liver and kidneys at 10, 20, and 30 days of age. Restriction of energy or protein intake from birth to 10 and 20 days of age prevented the normal increase in cell number in most of the organs studied. Protein to DNA ratio remained relatively constant for the thymus and lung throughout the experimental period. A comparison of DNA in organs of energy- and protein-restricted rats indicated that there were significantly fewer cells within the thymus of rats protein-restricted for 10 days and within the heart of rats restricted in protein for 20 days. Switching to an adequate diet after a 10 to 20 days restriction period stimulated cellular growth in both experimental groups. At 30 days of age, rats restricted for 10 days and rehabilitated for 20 days attained about 90% of the organ DNA of the controls. The rates of recovery in body weight and organ DNA were lower in rats restricted for 20 days and rehabilitated for 10 days. These data suggest that growth of individual organs during the first 20 days of life in rats is susceptible to protein and energy influences—the longer the restriction, the more severe the damage to the growth and development of the rat pups. As the protein-restricted rats suffered a more severe growth impairment and showed less improvement upon rehabilitation, it appears that protein is the major limiting factor in achieving normal cell number in the organs and body size in the early period of life.

KEY WORDS: • protein • energy • cell development

Manuscript received 24 May 1976.