Early changes in plasma hormones and metabolites during fasting in king penguin chicks

Chicks of the king penguin (Aptenodytes patagonica) can tolerate a fast of 4-6 months during the subantarctic winter. The aim of this work was to study their initial response to food deprivation. Nine chicks were starved for 18 days. Two phases of starvation were defined according to changes in the specific daily loss in body mass: it decreased by 92% in phase I (6.6 +/- 0.3 days) and remained steady and low in phase II. Phase I was marked by a large decline in protein utilization, indicated by decreases in plasma levels of alanine (58%), uric acid (89%) and urea (76%) together with a decrease in circulating corticosterone (60%) and thyroxine (75%). In phase I, plasma insulin concentration decreased (61%) in some birds, but did not change in others; plasma pancreatic glucagon was stable whereas gut-glucagon decreased by 75%. Free fatty acids and beta-hydroxybutyrate concentrations gradually rose during the fast to 5 to 6 times pre-fast levels. Glycemia remained unchanged. Phase II was characterized by no change in plasma concentrations of protein-derived metabolites and by no or little change in circulating hormone levels. From comparison with previous data, we conclude that there are similar early adjustments to food deprivation in king penguin chick, rat and man: (1) a decrease in resting metabolic rate, (2) a decrease in protein utilization, and (3) mobilization of fat stores. The key adaptations to long-term fasting in these species are therefore effectiveness in protein sparing and ability to prolong this situation.(ABSTRACT TRUNCATED AT 250 WORDS)