Abstract
The level of mRNA specific for myosin heavy chain in percutaneous biopsy specimens of skeletal muscle was analyzed in 6 healthy volunteers before and following 3 days of total starvation. Total RNA was isolated and hybridized to a radioactively labeled cDNA probe specific for myosin heavy chain of the beta type. Increasing concentrations of total RNA were applied to the membrane filters used in the hybridization analysis. Slopes of the linear function of radioactivity versus RNA concentration were calculated by linear regression. Following starvation the amount of hybridizable mRNA specific for myosin heavy chain decreased in relation to the total RNA. The decrease was individually specific, the mean value of the slopes after starvation being 91.6±2.8% that of the control (prestarvation) level (p<0.01). The low serum concentrations of insulin and C-peptide and the rise in glucagon together with the increase in urinary nitrogen excretion characterized the fasting condition of the 6 healthy volunteers. The analysis of mRNA specific for a single myofibrillar protein gave information on the physiological state of protein synthesis in muscle and indicated a fall in synthetic capacity due to the diminished availability of mRNA. The diminished level of myosin heavy chain mRNA in relation to total RNA confirmed previous findings of a decrease in muscle protein synthesis during short-term starvation. The decrease in mRNA added to the known decrease in ribosomal RNA.
