Studies on the measurement of whole-body protein degradation in vivo in the chicken.

1. An attempt was made to develop a new in vivo method for measuring whole-body protein degradation rate in chickens within an hour. For this purpose, two amino acid fluxes, absorption and protein synthesis were inhibited almost completely, followed by the measurement of changes in radioactivity and pool size in free amino acid pool. 2. The results indicated that the degradation rate estimated by the present direct isotope dilution method was not significantly different from that obtained by an indirect calculation based on the difference between the synthesis and net accretion rates in chicks fed ad libitum an adequate diet. 3. A computer-aided simulation analysis demonstrated that under the present circumstances incomplete inhibition of amino acid fluxes, i.e. absorption and protein degradation, affected the estimate of fractional rate of whole-body protein degradation, ranging from 75 to 110% of the experimentally-determined value.