Fasting/refeeding: an experimental model to study the impact of early thermal manipulation on hepatic metabolism in mule ducks.

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An increase in egg incubation temperature was previously shown to enhance the metabolism of mule ducks and increase liver fattening after overfeeding, through a metabolic programming mechanism. Here, we examined whether fasting (F) followed by refeeding (RF) in 11-wk-old mule ducks could become an accelerated model to study the mechanisms of metabolic programming following embryonic thermal manipulation. This study investigated the hepatic response of mule ducks subjected to 23 h of fasting and 1 h of refeeding, in control or thermally programmed animals (with an increase of 1°C, 16 h per day from days 13 to 27 of embryogenesis). Liver weight and energy composition, hepatocyte structure, plasma parameters, and gene expression levels were measured at 1, 2, and 4 h after RF. All these parameters were strongly affected by RF, whereas significant impacts of embryonic programming were measured in cell size (+1 µm on average), lipid composition (+4.2% of saturated fatty acids 4 h after the meal), and relative gene expressions (including HK1, SCD1, ELOVL6, and FASN). In addition to confirming previously identified molecular targets of thermal manipulation, this study revealed new ones, thanks to kinetic sampling after RF. Finally, the detailed description of the impact of the F/RF challenge on the liver structure, composition, and gene expression, but also on plasma parameters allowed us to draw a parallel with these same traits measured during overfeeding. This comparative analysis suggests that this protocol could become a pertinent model to study the mechanisms involved in embryonic liver thermal programming, without overfeeding.