Effects of dexamethasone on lung protein turnover.

Dexamethasone (2.5 mg/day per kg) treatment of young growing rats resulted in reduced food intake and rapidly inhibited whole-body and lung growth. Although the reduction in food intake partially explained the decrease in whole-body growth, it did not influence lung growth. After 24 h of dexamethasone treatment, ribosomal efficiency in the lung was reduced 44%, producing a 38% decrease in the rate of pulmonary protein synthesis. Extending dexamethasone treatment to 5 days resulted in decreases in both ribosomal efficiency (35%) and capacity (28%), explaining the 53% reduction in lung protein synthesis at this time. After both the acute and chronic steroid regimes, the decreased rates of pulmonary protein synthesis were accompanied by a loss of polyribosomes and an elevated ribosomal monomer pool, indicating that dexamethasone blocked translation at the site of peptide-chain initiation.