Stimulation of growth of the chick embryo by acute hyperoxia.

We have previously demonstrated that continuous incubation in elevated concentrations of ambient oxygen leads to accelerated growth of the chick embryo. We now report that a similar growth response is elicited by acute (72 h) exposure beginning on the 16th day of incubation. White Leghorn eggs were paired by initial weight and incubated in air for 15 days in forced-draft incubators. Embryos were sampled on days 11, 13 and 15 (experiments 1, 2, 3) or 13, 14 and 15 (experiment 4), freed of all extra-embryonic membranes and weighed. On day 16 the experimental group was switched to 60% O2. The control group was maintained in air. A portion of the remaining eggs from each group was opened on days 16, 17 and 18 (experiment 4), or alternatively all the remaining eggs were opened at the end of the 18th day of incubation (experiments 1, 2, 3). Linear regression analysis of growth curves obtained by plotting log wet embryo weight (g) vs log incubation age (d) showed a significantly greater rate of growth (slope) for days 15-18 in embryos exposed to 60% O2. These results support the hypothesis that growth of the chick embryo is normally limited by the availability of oxygen.