THE EFFECT OF HYPEROXIA ON EMBRYONIC AND ORGAN MASS IN THE DEVELOPINGCHICK-EMBRYO

It is known that hyperoxia stimulates growth late in incubation when t he chick embryo outgrows the O-2 diffusion capacity. We wondered wheth er hyperoxia could have an effect in the early period prior to the sta ge where metabolism exceeds the oxygen diffusion capacity of the eggsh ell. For this we studied four groups of chicken eggs: control group (C G; n = 100) and three test groups (TGs) exposed during 48 h to 60% O-2 on days 10, 14, and 18. In the CG, embryonic and organ mass (brain, h eart, lungs, liver and intestine) were measured from day 10 until day 21 of incubation. In the TGs embryonic and organ mass were obtained fr om 24 h after the start of hyperoxia exposure until the end of incubat ion. In all TGs the most striking growth rate acceleration was observe d in the liver and intestine, maximum growth rate accelerations were r espectively, 19 and 42% in TG1, 43 and 173% in TG2 and 39% and 84 in T G3. In contrast, the brain was little affected by the hyperoxia exposu re, the maximum growth rate acceleration was 14% in TG2. The results s uggest that also in the middle of the incubation period O-2 availabili ty can be a limiting factor for growth, before metabolism exceeds the oxygen diffusion capacity of the eggshell. (C) 1998 Elsevier Science B .V. All rights reserved.