Abstract
We investigated the aerobic scope of chicken embryos, that is, the margin of increase of oxygen consumption (V̇O2) above its normal value. V̇O2 was measured by an open-flow methodology at embryonic ages E3, E7, E11, E15, E19 and at E20 at the internal (IP) and external pipping (EP) phases, at the normal incubation temperature (Ta=38°C), in hypothermia (Ta=30°C) and in hyperthermia (Ta=41 and 44°C). In the cold, Q10 averaged ~2 at all ages, except in IP and EP when lower values (~1.5) indicated some degree of thermogenesis. In hyperthermia (38–44°C) Q10 was between 1 and 1.4. Hyperthermia had no significant effects on V̇O2 whether the results combined all ages or considered individual age groups, except in IP (in which V̇O2 increased 8% with 44°C) and EP embryos (+13%). After opening the air cell, which exposed the embryo to a higher O2 pressure, hyperthermic V̇O2 was significantly higher than in normothermia in E19 (+13%), IP (+22%) and EP embryos (+22%). We conclude that in chicken embryos throughout most of incubation neither heat nor oxygen availability limits the normal (normoxic-normothermic) values of V̇O2. Only close to hatching O2-diffusion represents a limiting factor to the embryo's V̇O2. Hence, embryos differ from postnatal animals for a nearly absent aerobic scope, presumably because their major sources of energy expenditure (growth and tissue maintenance) are constantly maximized.
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More From: Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology
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