Carbohydrates affect protein-turnover rates, growth, and nucleic acid content in the white muscle of rainbow trout ( Oncorhynchus mykiss)

Abstract

We have investigated the effect of dietary carbohydrate on different parameters of protein-turnover rate, nature of growth, and nucleic acid content in the muscle of rainbow trout in order to better understand the molecular nature of these growth parameters in the absence of this dietary component. For this, we used a methodology based on the incorporation rate of tritium labelled phenylalanine in muscle protein. Juvenile rainbow trout of an initial body weight of 110 g were fed near to satiety with a control or a non-carbohydrate diet during 7 weeks. The absence of dietary carbohydrate significantly depressed fish growth, as well as daily body weight gain, as a consequence of muscular hypotrophy (the cell size diminished by almost 50%) and not by a reduction of number of cells (hypoplasia). This nutritional situation also significantly slowed (by almost 11%) muscle-protein accumulation rate ( K G) as a result of a significant increase (eight-fold) in muscle-protein degradation rate ( K D), without changing the other protein-turnover rates, protein synthesis rate ( K S), protein synthesis capacity ( C S), protein synthesis efficiency ( K RNA), protein synthesis rate per cell unit ( K DNA), or protein retention efficiency (PRE). These results, together with the nucleic acid content, clearly indicate that the absence of carbohydrate significantly exacerbates the muscular-protein degradation without affecting protein synthesis. In conclusion, carbohydrates are needed to prevent amino acids released during protein degradation from being used to synthesize carbohydrates and/or to be used for energy and not for growth.