Skeletal muscle RNA synthesis following endurance and sprint exercise.

Two groups of male Wistar endurance- and sprint-acclimatized rats were used to study the time course of uridine uptake into skeletal muscle RNA following acute exercise. Endurance and sprint animals were killed at 0, 2, 18, 24, and 48 hr following 1 hr of either endurance (30 m X min-1) or sprint running (90 m X min-1). Red vastus (RV) and white vastus (WV) muscle samples were incubated for 30 min in a medium containing 1 microCi 5-[14C]uridine. Uridine uptake was determined in the myofibrillar-nuclear, mitochondrial, microsomal, and soluble fractions of skeletal muscle via liquid scintillation counting. A significant decrease in whole muscle uridine uptake into RNA was observed in RV muscles following endurance exercise as well as in WV of sprint-exercised rats. Sprint-exercised RV had significantly greater uridine uptake into RNA in the homogenate and myofibrillar-nuclear fraction 2-18 hr post exercise. Increased mitochondrial uridine incorporation into RNA was observed in endurance- and sprint-exercised muscles between 18 and 48 hr post exercise. A very large increment in microsomal uridine uptake was observed in sprint-exercised WV at 24 hr. These data suggest that while whole muscle RNA synthesis may decline immediately following acute exercise overload, increases are observed in specific muscle fractions. These changes appear to coincide with protein-specific adaptations to sprint and endurance exercise.