Tissue protein turnover is altered during catch-up growth following Escherichia coli infection in weanling rats.

Infection in young growing animals is manifested by poor tissue protein accretion; during subsequent catch-up growth this is reversed. To account for these changes, protein synthesis and degradation were measured in vivo in skeletal muscle, skin, liver and small intestine in weanling rats during catch-up growth after Escherichia coli infection. Observations were made at d 4, 6, 8, 11 and 14, when infected rats had elevated nitrogen balance. Liver protein mass and turnover were not affected by treatment. Although protein mass of small intestine fell during infection, catch-up was achieved before d 4, suggesting a high priority for protein repletion in this tissue. On d 4, protein mass was lower (P < 0.05) in muscle (-19%) and skin (-23%) in infected vs. control rats. Thereafter growth rates of skeletal muscle and skin were higher (P < 0.001) in infected rats compared with controls. Catch-up growth was most pronounced early, but continued throughout the study. During catch-up growth, protein synthesis (mg/d) in muscle and skin was not different between control and infected animals. Protein synthesis was maintained in muscle because RNA mass was maintained. During catch-up growth in muscle and skin of infected rats, there was lower protein degradation (mg/d) than in controls (P < 0.05). We conclude that alterations in protein turnover during catch-up growth are tissue and time dependent and are different from those described in other hyperanabolic states.