Cellular Response in Rats during Malnutrition at Various Ages

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Abstract
Malnutrition retards growth in animals and children. Recovery of normal stature on refeeding depends, in part, on age at onset of deprivation. To investigate the cellular events underlying this time-dependence, rats were exposed to 21 days of caloric restriction at birth, at weaning and at age 65 days and then refed normally until adulthood. Total organ weight, protein, RNA, and DNA were measured during the periods of caloric restriction and subsequent refeeding. Total organ DNA and weight/DNA, protein/DNA, and RNA/DNA ratios in test and control animals reared in the usual manner served as indexes of changes in organ cell size and number. Malnutrition from birth to weaning resulted in a proportional decrease in weight, protein, RNA, and DNA, indicating a reduction in cell number without alteration in cell size. These animals did not recover normal growth when adequately refed. Malnutrition from weaning to 42 days of age resulted in a proportional reduction in weight, protein, RNA, and DNA in all organs except brain and lung. Although weight, protein, and RNA were reduced in these 2 organs, DNA was unaffected. Refeeding was accompanied by recovery in weight of these 2 organs only, resulting in an animal retarded in overall growth with normal-size brain and lung. Finally, malnutrition from 65 to 86 days of age resulted in maintenance of DNA values in all organs except spleen and thymus, whereas weight, protein, and RNA were reduced. The reduced ratios coupled with normal DNA suggest decrease in cell size with retention of cell number. All organs in the animals except thymus recovered normal size on refeeding and all ratios returned to normal. These data suggest that cellular effects of malnutrition depend on the phase of growth in the animal at the time of malnutrition. Early malnutrition impeded cell division and the animal did not recover. Malnutrition at a later stage of growth resulted in reduction of cell size from which the animal could recover.