Oxygen uptake and chorioallantoic blood flow changes during acute hypoxia and hyperoxia in the 16 day chicken embryo

Abstract

Oxygen consumption rate (Ṁ O 2 of hen eggs was measured on incubation day 16 (37.8°C, 55% humidity) during acute exposure (90 min) to ambient hyperoxia (Fl O 2 = 0.42) or hypoxia (Fl O 2 = 0.105). During the last part of these exposures, an H 2 washout method was used to estimate relative changes in chorioallantoic membrane (CAM) blood flow, taking as an index the net change in the H 2 washout rate constant between any experimental condition and the circulation arrested egg. Doubling normoxic Fl O 2 increased Ṁ O 2 to an asymptotic value which was 4% above the normal ( P < 0.05; Ṁ O 2 in normoxia = 890 μmol/h) even after correcting for the normoxic increase in Ṁ O 2 with time during development ( Δ M ̇ O 2 /Δ t = 21.5 μ mol/h 2; P < 0.001 ). Halving Fl O 2 ralculated in the same way to 388 μmol/h. The estimate of the CAM blood flow, relative to normaxia, was 1.12 in hyperoxia (not significant, P = 0.05) and 0.68 in hypoxia ( P < 0.001). The limited changes in CAM blood flow and Ṁ O 2 during hyperoxia indicate that they are both already close to their maximal values in normoxia. During acute hypoxia the 16 day embryo behaves as an oxygen-conformer; however, the small relative decrease in Ṁ O 2 per unit of the flow index observed during hyperoxia suggests that the embryo can regulate its CAM blood flow to a small extent. The survival of the embryo and its recovery from hypoxia without a detectable O 2 repayment suggest small if any anaerobic regulatory pathways and indicate a true metabolic depression.