Twelve generations of marginal protein deficiency

Abstract

1. Colonies of rats have been maintained for twelve generations on diets adequate (dietary-protein energy:total metabolizable energy (NDp:E) 0·I) or marginally deficient in protein (NDp:E 0·068)2. In the malnourished colony, the proportion of ‘small-for-gestational-age’ offspring was ten times as high as amongst the well-nourished colony, growth was slow, sexual maturation delayed, especially in the females, and, when adult, both sexes were significantly lighter and shorter than adults of the well-nourished colony. Organs, other than the eye, weighed less than those of well-nourished ‘age’ controls, but when expressed relative to body-weight, the brain, pituitary, thyroid, adrenals, testes, thymus and eyes were larger, the pancreas unchanged and the kidneys smaller than those of the well-nourished ‘age’ controls. The relative weight of the liver showed little change, being slightly increased in the males and, like the ovaries, slightly reduced in the females. On a body-weight basis, the brains were about 50% heavier than normal, but in absolute terms were 5–5·5% lighter than those of the well-nourished animals, the cerebellum (10·5% lighter in males and 12·9% lighter in females) being more severely affected than the cerebrum (4% lighter)3. The young malnourished rats showed increased exploratory activity, transient head tremors and an increased sensitivity to noise, the latter being long-lasting if not permanent. When adult, they showed marked differences in behaviour and learning patterns and it was difficult to attract and hold their attention. In situations demanding a choice the animals were very excited, emitted loud squeals and tried to escape from what was clearly a stressful situation. However, a casual examination of the malnourished adults revealed a rather small, badly groomed, excitable rat without gross abnormalities4. The findings are discussed in relation to changes found in malnourished human communities.