Muscle protein turnover in sex-linked dwarf and normal broiler chickens.

Dietary infusion of L-[U-14C]tyrosine was used to estimate the fractional protein synthesis rates (FSR) in normal and dwarf female broiler chicks. Five 2-week-old and five 3-week-old birds of each genotype were placed in individual metabolism cages and given a purified diet in agar-gel containing 2 mu Ci L-[U-14C]tyrosine for 6 hr. Birds were killed and the pectoralis major (PM) and combined gastrocnemius and peroneous longus muscles (LM) were removed for analyses. Additional groups of 4 to 5 chickens were killed 3 days before and 3 days after each infusion to determine fractional protein accretion rate (FAR) over the 6-day period. Fractional degradation rate (FDR) was obtained by difference (FDR = FSR - FAR). Protein, ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) concentrations were determined to observe possible relationships between these cellular constituents and FSR. Activities of RNA and DNA were determined as units of protein synthesized per unit RNA or DNA per day. Two-week-old chicks, dwarf chicks, and the PM muscles had higher (P less than .05) FSR than 3-week-old chicks, normal chicks, and the LM, respectively. Two-week-old chicks and dwarf chicks had higher FDR than 3-week-old chicks, respectively. There was a significant decrease in RNA concentration and RNA activity from 2 to 3 weeks. The RNA activity tended to be higher in dwarf than normal birds. Concentration of RNA was higher (P less than .05) in the PM than LM. However, DNA concentration was higher (P less than .05) in the LM than PM.(ABSTRACT TRUNCATED AT 250 WORDS)