AJP - Endocrinology and Metabolism, Vol 251, Issue 4 379-E384, Copyright © 1986 by American Physiological Society
Protein degradation in skeletal muscles after evisceration of fed or fasted rats
O. L. Smith
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.
