Marginal congenital malnutrition on skeletal muscle composition.

Experiments were performed on well fed and marginally malnourished rats from a black and white hooded strain bred for 11 generations. The colony on high protein diet was fed a well balanced cubed diet of net dietary protein energy ratio 10% (Diet F1). The other colony was fed a cubed diet of net dietary protein energy ratio 6.8% (Diet F2). This latter diet is inadequate to maintain normal growth of young rats but adequate for the maintenance of adult life. The animals were killed at various ages from weaning until they aged 330 days. At various time points, the gastrocnemius muscle was excised quantitatively and analysed for RNA. Analyses were also made for DNA and protein and the results were discussed in terms of RNA/DNA, protein/DNA and RNA/protein ratios. During normal growth and development, there was pronounced reduction in the RNA/protein ratio in both colonies similar to reported developmental changes on the rate of protein synthesis. The cause of failure of the "catch up" growth of the marginally malnourished rats was not reduction in RNA concentration but reduction in nuclear proliferation and protein accumulation leading to hyperplastic and hypertrophic growth failures at most stages.