Abstract
The control of hepatic metabolism by substrates and hormones was assessed in perfused liver from young Muscovy ducklings. Studies were performed in fed or 24-h fasted 5-week-old thermoneutral (25°C; TN) or cold-acclimated ducklings (4°C; CA) and results were compared with those obtained in rats. Basal oxygen uptake of perfused liver (LVO 2) was higher after cold acclimation both in fed (+65%) and 24-h fasted (+29%) ducklings and in 24-h fasted rats (+34%). Lactate (2 mM), the main gluconeogenic substrate in birds, similarly increased LVO 2 in both TN and CA ducklings and the effect was larger after fasting. Both glucagon and norepinephrine dose-dependently increased LVO 2 in ducklings and rats, but cold acclimation did not improve liver response and liver sensitivity to norepinephrine in ducklings was even reduced in CA animals. Liver contribution to glucagon-induced thermogenesis in vivo was estimated to be 22% in TN and 12% in CA ducklings. Glucagon stimulated gluconeogenesis from lactate in duckling liver and the stimulation was 2.2-fold higher in CA than in TN fasted birds. These results indicate a stimulated hepatic oxidative metabolism in CA ducklings but hepatic glucagon-induced thermogenesis (as measured by LVO 2) was not improved. A role of the liver is suggested in duckling metabolic acclimation to cold through an enhanced hepatic gluconeogenesis under glucagon control.
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