Semi-starvation alters myofibrillar mRNA concentrations to expedite rapid recovery of muscle protein stores following feeding

Background Protein synthesis in skeletal muscle is reduced following starva tion and restored by feeding. The mediators and mechanisms are incompletely understood. The aim of this study was to evaluate whether prolongation of undernutrition induced changes in muscle gene expression at the level of mR NA and protein. Materials and methods The changes in myosin heavy-chain 2X mRNA in adult pa rtially starved (50% of ad libitum standard rodent chow intake for 4 or 7 d ays) C57BL mice or subsequently refed mice were studied. Ad libitum-fed mic e were used as controls. Protein synthesis, total RNA and myosin heavy-chai n 2X mRNA concentrations were determined. Plasma concentrations of amino ac ids were measured by high-performance liquid chromatography. Results Partial starvation of 4 and 7 days reduced body weight by 15.6 +/- 1% and 17.1 +/- 2.1% (P less than or equal to 0.05) vs. ad libitum fed cont rols. Protein synthesis was reduced by 32 +/- 9% and protein content by 20 +/- 4% (P less than or equal to 0.05) following 7 days of partial starvatio n. Plasma amino acid concentrations were increased (6297 +/- 853) in refed animals vs. ad libitum-fed controls (3057 +/- 141, P less than or equal to 0.05). Total RNA concentration (mu g RNA mu g(-1) DNA) in skeletal muscle w as unchanged. Myosinheavy-chain 2X mRNA concentration did not change follow ing 4 days of partial starvation but increased by 24 +/- 5% (P less than or equal to 0.05) following 7 days of partial starvation, hence suggesting th at expression of myosin mRNA was nutritionally altered. Conclusion Postprandial stimulation of protein synthesis following starvati on may thus be a combination of increased mRNA availability and increased t ranslation. This effect may be activated by peak concentrations of amino ac ids in plasma following feeding.