Glycerol and NEFA kinetics in long-term fasting king penguins: phase II versus phase III.
In spontaneously fasting birds such as penguins, below a body mass threshold corresponding to the phase II-phase III transition, a metabolic and hormonal shift occurs and feeding behaviour is stimulated ('refeeding signal'). The major aim of this study was to determine whether a decrease in non-esterified fatty acid (NEFA) release from adipose tissue could be a component of this signal. Lipolytic fluxes and primary triacylglycerol:fatty acid (TAG:FA) cycling were determined in vivo in breeding, fasting king penguins (Aptenodytes patagonicus) using continuous infusions of 2-[3H]glycerol and 1-[14C]palmitate under field conditions. In phase II (after approximately 8 days of fasting, large fat stores, body protein spared, N=8), the rate of appearance (R(a)) of glycerol and of NEFA were 5.7+/-0.8 and 10.5+/-0.4 micromol kg(-1) min(-1), respectively, and the percentage of primary TAG:FA cycling was 41+/-7%. In phase III (after approximately 25 days of fasting, fat stores reduced by fourfold, increased body protein catabolism, N=9), R(a) glycerol kg(-1) body mass remained unchanged, whereas R(a) glycerol kg(-1) fat mass and R(a) NEFA kg(-1) body mass were increased by 2.8-fold and 1.5-fold, respectively. Increased R(a) glycerol kg(-1) fat mass was possibly the result of a 3.5-fold increase in circulating glucagon, the increased R(a) NEFA kg(-1) body mass being attributable to decreased primary TAG:FA cycling. Thus, triggering of the refeeding signal that redirects the behavior of fasting, incubating penguins from incubation towards the search for food after entrance into phase III cannot be ascribed to a reduction in lipolytic fluxes and NEFA availability.
Bernard
S F
SF
Centre d'Ecologie et Physiologie Energétiques, Centre National de la Recherche Scientifique, 67087 Strasbourg, France.
Fayolle
C
C
Robin
J-P
JP
Groscolas
R
R
D000818:Animals; D001717:Birds / Q000378:metabolism* / Q000502:physiology; D005215:Fasting / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005247:Feeding Behavior / Q000502:physiology; D005990:Glycerol / Q000378:metabolism*; D007700:Kinetics; D008066:Lipolysis; D008297:Male; D014280:Triglycerides / Q000378:metabolism
D005230:Fatty Acids, Nonesterified; D014280:Triglycerides; D005990:Glycerol