Glycerol and NEFA kinetics in long-term fasting king penguins: phase II versus phase III

• Published in: Journal of experimental biology Vol. 205; no. Pt 17; pp. 2745 - 2754
• Main Authors: Bernard, S F, Fayolle, C, Robin, J-P, Groscolas, R
• Format: Journal Article
• Language: English
• Published: England 01.09.2002
• Subjects: Animals; Aptenodytes patagonicus; Birds - metabolism; Birds - physiology; Fasting - metabolism; Fatty Acids, Nonesterified - metabolism; Feeding Behavior - physiology; Glycerol - metabolism; Kinetics; Lipolysis; Male; Triglycerides - metabolism
• ISSN: 0022-0949; 1477-9145
• DOI: 10.1242/jeb.205.17.2745

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.