Protein degradation in skeletal muscles after evisceration of fed or fasted rats

To test the rate of protein degradation in muscles under more physiological conditions, in vitro methods were adapted for use in rats whose skeletal muscles had been isolated intact by an evisceration procedure. Under pentobarbital anesthesia the vessels to the gastrointestinal tract were ligated, the organs removed, and the liver left in situ. Normal rectal temperature was maintained, glucose was given to prevent hypoglycemia and the animals were studied for a 2-h period. For the present experiments, evisceration was carried out after protein synthesis was blocked with cycloheximide so that the accumulation of the amino acid tyrosine (not metabolized) in the plasma of the preparation could be used to indicate the rate protein was degraded in the peripheral tissues. When normal fed rats (270 g) were eviscerated, the concentration of plasma tyrosine increased postoperatively, but, if the rats were fasted 20 h and then eviscerated, tyrosine accumulation was significantly enhanced. After 2 h, it was 50% greater than in the fed controls. Refeeding for 3 h completely prevented this effect. The results suggest that the rate of overall skeletal muscle protein degradation can be measured by the use of eviscerated rats and that this rate is sensitive to short periods of food deprivation.