Effects of largely different feeding intensities on serum insulin-like growth factor-1 concentrations, quantified by enzyme immunoassay, leptin and growth hormone receptor 1 mRNA in rainbow trout (Oncorhynchus mykiss)

Abstract

Insulin-like growth factor-1 (IGF-1), somatolactin and leptin are involved in growth regulation and energy metabolism in fish. We herein focused on serum IGF-1 concentration analysed by enzyme-linked immunosorbent assay in restrictively fed rainbow trout (Oncorhynchus mykiss). The animals were fed a high-fat/low-protein diet at daily feed increases (DFI) ranging from 0.5% to 2% of initial body weight (IBW), starting either at 62 or 176 g IBW. In selected groups, growth hormone receptor 1 (GHR1) and leptin mRNA were quantified in liver, and GHR1 mRNA also in visceral adipose tissue. Serum IGF-1 concentrations in both IBW groups were highest at 2% and 1% DFI and were nonlinearly decreasing with reduced DFI. The low-IBW groups had mostly lower IGF-1 concentrations than the high-IBW groups. Leptin and GHR1 mRNA decreased with feeding intensity in liver, but GHR1 mRNA increased in adipose tissue. IGF-1 is related to growth and may help to mitigate oxidative stress in consequence of lipid mobilization during restrictive feeding. IGF-1 secretion associated with stress response in addition to its function in growth and energy metabolism seemed to reach a point of inflection at DFI 1%. Leptin and GHR1 might be linked to lipid metabolism and free fatty acid partitioning towards liver.