Fasting in king penguin. I. Hormonal and metabolic changes during breeding

Abstract

During long-term fasting in birds and mammals, protein utilization initially decreases (phase I), is thereafter maintained at a low value (phase II), and then further increases (phase III). To delineate hormonal and biochemical changes responsible for these modifications, the effect of food deprivation for 50 days was studied in 6 male king penguins captured at the beginning of their natural breeding fast. During phase II, both rate of mass loss and plasma uric acid concentration remained at low levels, whereas plasma beta-hydroxybutyrate concentration increased. In phase III there was by contrast a 2.5-fold increase in the rate of mass loss, an eightfold increase in plasma uric acid, and an 80% drop in plasma beta-hydroxybutyrate. Plasma corticosterone was low and steady in phase II and increased three times in phase III. During the overall fast, there were no significant variations in plasma insulin, but there was a fourfold increase in plasma glucagon and a decrease in plasma thyroxine and triiodothyronine. These findings suggest that protein sparing (phase II) requires low levels of corticosterone, insulin, and thyroid hormones, whereas the further increase in protein utilization (phase III) is due to an increase in plasma corticosterone. The high plasma glucagon concentration in phase III is presumably responsible for a transient increase in plasma glucose observed at this stage; such increase in glucagon could enhance gluconeogenesis from amino acids.

Factors Affecting Plasma Concentrations of Prolactin in the Common Eider Somateria mollissima

“…Likewise, we did not find a direct relationship between body mass and prolactin levels in incubating female eiders, because the birds seldom reach a phase III during normal incubation (Criscuolo et al, 2001). Such a result is consistent with the incubation strategy of capital incubators, which because they depend almost exclusively on their endogenous nutrient reserves are able to lose a large amount of body mass without threatening their reproduction or survival (Cherel et al, 1988;Moreno, 1989). On the other hand, a deteriorated adult body condition at hatching could have an impact on the posthatch parental behavior.…”

“…Phase II corresponds to a long period of economy, during which the rate of body mass loss and the body protein utilization are low, most of the energy being derived from lipids. Phase III is critical because both rates of body mass loss and protein utilization are increasing while body lipids neared depletion (Cherel et al, 1988).…”

Baseline and Stress‐Induced Levels of Corticosterone during Different Life Cycle Substages in a Shorebird on the High Arctic Breeding Grounds

“…For example, in a study of 10 passerine species caught in the spring on an Italian island just after a migratory flight of at least 500 km from North Africa, only individuals with depleted fat stores and critically emaciated breast muscles (an important source of protein) showed high corticosterone levels (!45 ng/mL; Jenni et al 2000)-levels that were suggested to be associated with increased protein breakdown, as in voluntarily fasting king penguins (Aptenodytes patagonica; Cherel et al 1988). Red knots are usually thought to arrive on the breeding grounds with some fuel (fat and protein) stores remaining (Davidson and Evans 1988;Davidson and Morrison 1992).…”

Glucose utilization rate and pancreatic hormone response to oral glucose loads are influenced by the migratory condition and fasting in the garden warbler (Sylvia borin)

“…However, this does not seem to apply for seasonal fattening species like the garden warbler, which show no corticosterone increase while drawing on lipid reserves (Cherel et al 1988, Schwabl et al 1991.…”