Stimulation of actin and myosin synthesis in rat gastrocnemius muscle by clenbuterol; evidence for translational control.

Abstract 1. A transient rise in fractional rates of protein and actomyosin synthesis was observed in gastrocneumius muscles of rats fed clenbuterol for 1–2 days but the muscle RNA: protein ratio was unchanged, therefore protein synthesis per unit RNA ( k RNA ) also increased. 2. Myosin heavy and light chains and actin showed increased incorporation of [ 3 H]phenylalanine at 2 days; these changes were proportional to increases in total protein synthesis. 3. The ratios actin mRNA: 18S RNA and fast myosin heavy chain mRNA: 18S RNA were unaffected by clenbuterol. 4. The data suggest that the clenbuterol-induced increase in muscle protein synthesis involves both translational control and increased tissue RNA.