Embryos and extraembryonic membranes recovered from the sheep conceptus on Days 13, 15, 17 and 19 of pregnancy were incubated in medium containing glucose as sole energy substrate. In all components of the conceptus 60-70% of substrate carbon incorporated was recovered in the nonglycogen acid-soluble fraction, 25-30% in non-glycogen macromolecules and 4-8% in the glycogen pools. At all stages of development examined, embryonic tissue accumulated more glucose carbon into all fractions than did yolk sac which in turn was more active than trophoblast. After its appearance, the allantois was at least as active in glucose incorporation as embryonic tissue. Over the period of development examined, incorporation into all tissues of the conceptus fell progressively as pregnancy advanced and, by Day 19, total incorporation was about 60% of the initial value for each component.Reduction in oxygen concentration generally depressed incorporation into all intracellular carbon pools. The most consistent and significant effects were recorded for the two non-glycogen pools where incorporation fell, on average, by 30-40% when 02 concentration was reduced to 1%. Most of the response observed was due to a drop in 02 concentration from 20 to 5% with smaller additional effects when the 02 was further reduced to 1%. Incorporation into all pools isolated tended to follow a similar pattern and incorporation into the three macromolecular components, expressed as a percentage of total incorporation, remained unchanged as 02 concentration was reduced
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