Selective changes in the protein-turnover rates and nature of growth induced in trout liver by long-term starvation followed by re-feeding

We report upon the effects of a cycle of long-term starvation followed by r e-feeding on the liver-protein turnover rates and nature of protein growth in the rainbow trout (Oncorhynchus mykiss). We determined the protein-turno ver rate and its relationship with the nucleic-acid concentrations in the l ivers of juvenile trout starved for 70 days and then re-fed for 9 days. Dur ing starvation the total hepatic-protein and RNA contents decreased signifi cantly and the absolute protein-synthesis rate (A(S)) also fell, whilst the fractional protein-synthesis rate (K-S) remained unchanged and the fractio nal protein-degradation rate (K-D) increased significantly. Total DNA conte nt, an indicator of hyperplasia, and the protein:DNA ratio, an indicator of hypertrophy, both fell considerably. After re-feeding for 9 days the prote in-accumulation rates (K-G, A(G)) rose sharply, as did K-S, A(S), K-D, prot ein-synthesis efficiency (K-RNA) and the protein-synthesis rate/DNA unit (K -DNA). The total hepatic protein and RNA contents increased but still remai ned below the control values. The protein:DNA and RNA:DNA ratios increased significantly compared to starved fish. These changes demonstrate the high response capacity of the protein-turnover rates in trout liver upon re-feed ing after long-term starvation. Upon re-feeding hypertrophic growth increas ed considerably whilst hyperplasia remained at starvation levels.