Glucose regulates lipid metabolism in fasting king penguins

Abstract

This study aims to determine whether glucose intervenes in the regulation of lipid metabolism in long-term fasting birds, using the king penguin as an animal model. Changes in the plasma concentration of various metabolites and hormones, and in lipolytic fluxes as determined by continuous infusion of [2-3H]glycerol and [1-14C]palmitate, were examined in vivo before, during, and after a 2-h glucose infusion under field conditions. All the birds were in the phase II fasting status (large fat stores, protein sparing) but differed by their metabolic and hormonal statuses, being either nonstressed (NSB; n = 5) or stressed (SB; n = 5). In both groups, glucose infusion at 5 mg.kg-1.min-1 induced a twofold increase in glycemia. In NSB, glucose had no effect on lipolysis (maintenance of plasma concentrations and rates of appearance of glycerol and nonesterified fatty acids) and no effect on the plasma concentrations of triacylglycerols (TAG), glucagon, insulin, or corticosterone. However, it limited fatty acid (FA) oxidation, as indicated by a 25% decrease in the plasma level of beta-hydroxybutyrate (beta-OHB). In SB, glucose infusion induced an approximately 2.5-fold decrease in lipolytic fluxes and a large decrease in FA oxidation, as reflected by a 64% decrease in the plasma concentration of beta-OHB. There were also a 35% decrease in plasma TAG, a 6.5- and 2.8-fold decrease in plasma glucagon and corticosterone, respectively, and a threefold increase in insulinemia. These data show that in fasting king penguins, glucose regulates lipid metabolism (inhibition of lipolysis and/or of FA oxidation) and affects hormonal status differently in stressed vs. nonstressed individuals. The results also suggest that in birds, as in humans, the availability of glucose, not of FA, is an important determinant of the substrate mix (glucose vs. FA) that is oxidized for energy production.

High Corticosterone, Not High Energy Cost, Correlates with Reproductive Success in the Burrow-Nesting Ancient Murrelet

“…RQ index provides an indication of the principal substrates being utilized [54] . In our study the initial RQ index indicated that, as expected, fat was the main energy resource during fasting for murrelets [55] , [56] . RQ increased with date, perhaps indicating a change in energy sources from capital (less protein) to income (more protein) breeding [8] .…”

Effects of nest type and sex on blood saccharide profiles in Humboldt penguins (Spheniscus humboldti): Implications for habitat conservation

“…Plasma corticosterone responses to handling were similar in great tit and Adélie penguin [77], and Magellanic penguin chicks exposed to tourists had elevated corticosterone stress responses relative to undisturbed chicks in the same breeding colony [78]. In phase II fasting status king penguins under field conditions, noise from human activity affected glucose regulation of lipid metabolism and decreased plasma glucagon 6.5-fold and corticosterone 2.8-fold [52]. We project similar differences in gene expression between Humboldt penguins in unsheltered and sheltered nests.…”

“…Glucose regulates lipid metabolism in penguins and affects hormonal status differently in stressed and non-stressed individuals [52]. For example, stress due to prolonged fasting is characterized by protein sparing and decreased energy expenditure, whereas stress due to molt is distinguished by increased catabolism of body protein and energy expenditure [53].…”

Glucose regulation is a repeatable trait affected by successive handling in zebra finches

“…Glucose is an important source of energy for several tissues. In vertebrates, its regulation involves the coordinated action of multiple organs and has an impact on protein and lipid metabolism (Hazelwood 2000;Bernard et al 2003;Braun and Sweazea 2008). Thereby, glucose regulation is a life sustaining process and variations in this process may affect individual's performance (Hazelwood 2000;Bernard et al 2003;Braun and Sweazea 2008;Scanes 2015; but see Ramenofsky 1990).…”

“…In vertebrates, its regulation involves the coordinated action of multiple organs and has an impact on protein and lipid metabolism (Hazelwood 2000;Bernard et al 2003;Braun and Sweazea 2008). Thereby, glucose regulation is a life sustaining process and variations in this process may affect individual's performance (Hazelwood 2000;Bernard et al 2003;Braun and Sweazea 2008;Scanes 2015; but see Ramenofsky 1990). An effective response of glucose regulation is recognized as a hallmark of health in humans and laboratory models, and its impairment has been linked to mechanisms associated with the ageing process (Gardner et al 2005;Semba et al 2010;Picard et al 2014;Regan et al 2020).…”