February 15-18, 2009 Washington State Convention Center Seattle ...

EFFECT OF FEED DEPRIVATION AND INSULIN-LIKE GROWTH HORMONE ON INDICES
OF PROTEIN DEGRADATION IN RAINBOW TROUT (Oncorhynchus mykiss)
Beth M. Cleveland*, Gregory M. Weber, Kenneth P. Blemings and Jeffrey T. Silverstein
National Center for Cool and Cold Water Aquaculture
ARS-USDA
11861 Leetown Rd.
Kearneysville, WV 25430 USA
beth.cleveland@ars.usda.gov
Insulin-like growth factor-I (IGF-I) is a hormone that promotes growth by both increasing protein synthesis and decreasing
protein degradation. This study utilizes a comparative slaughter approach to determine the effect of feed deprivation and IGF-I
treatment on weight loss and indices of protein degradation. Knowing how proteolytic pathways are affected by nutrient deprivation
and IGF-I will contribute to the understanding of the impact and regulation these pathways have on protein turnover.
Two yearling fish from each of eight rainbow trout families were stocked into 35 30-gallon tanks that were randomly assigned
to five treatment groups (n=7). One treatment group was harvested on day 1 and fish in 14 tanks were implanted with an osmotic
pump containing either recombinant human IGF-I (25 ug/kg/d) or saline. All fish that received impants (2 groups) and an
additional treatment group of fish were harvested after 14 days of feed deprivation. The final treatment group was harvested after
28 days of feed deprivation. For each tank one fish from each family was kept whole for proximate analysis while liver and
white muscle samples were snap frozen for gene expression analysis and blood was collected for 3-methylhistine detection.
Fish treated with IGF-I lost less weight than untreated fish after 14 days of feed deprivation, however, dry weight and fat loss
were not significantly affected by IGF-I treatment (Table 1). A reduction in the mRNA abundance of genes in the proteosome
and cathepsin pathways was observed in IGF-I treated fish (Table 2), indicating that the IGF-I mediated reduction in weight
loss during starvation may involve regulation of these two pathways. Genes in all proteolytic pathways were affected by the
duration of feed deprivation (Table 2). These data indicate that nutrient availability and IGF-I can regulate specific proteolytic
pathways in rainbow trout.
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