Organ growth in chick embryos incubated in 40% or 70% oxygen

Incubation of eggs in 60% oxygen has been shown to enhance growth of the chick embryo. To determine whether oxygen accelerates growth over a range of concentrations, eggs were incubated in 40% or 70% O2. Control eggs, pair-matched by initial weight, were simultaneously incubated in room air (21% O2). Embryo and organ weights from matched pairs of eggs were compared on incubation days 14, 16 and 18 (40% O2) or 10, 12, 14, 16 and 18 (70% O2). Embryos incubated in 40% O2 displayed a pattern of growth enhancement similar to that previously reported for 60% O2. Accelerated embryonic growth was maintained through day 18. The heart showed the greatest percentage increase in weight over control, exceeding that of the whole embryo on days 16 and 18. The brain displayed significant enhancement only on day 16. Weight of the liver was unaffected by hyperoxia. Embryos in 70% O2 exhibited accelerated growth in all of the tissues examined early in incubation. Growth rate of the hyperoxic embryos then declined, so that embryo weight on day 18 did not differ from control. The brain, heart, eye, and proventriculus plus gizzard from 70% O2 embryos weighed significantly less than controls on day 18. Growth inhibition was most striking in the heart; heart/body weight ratio of 70% O2 embryos was significantly less than control throughout the observation period. The results confirm the growth accelerative effect of oxygen and suggest that the degree of growth enhancement is proportional to the ambient oxygen concentration. Accelerated growth cannot be maintained, however, in 70% O2.