Incorporation of substrate carbon from [U-14C]acetate by the sheep conceptus recovered from the uterus on days 13 to 19 of pregnancy.

Of the substrate carbon incorporated from 1.12 mM [U-14C]acetate as sole energy substrate during a 2.5-h incubation, a large proportion was isolated in the acid-soluble fraction. Although there was no significant change over time in the rate of entry into this pool for embryos, the rate of accumulation by the trophoblast and yolk sac increased as development progressed. At Days 13 and 15 of pregnancy, incorporation of acetate into the acid-insoluble fraction of embryos accounted for almost half the total label accumulated. The rate of this incorporation fell rapidly over time and by Day 19 less than 30% of carbon accumulated was in this fraction. By contrast, the rate of incorporation into this fraction by trophoblastic tissue was low at Day 13 but rose dramatically as development progressed. Incorporation by the yolk sac into acid-insoluble components also rose with time. At the early stages of pregnancy studied, lipid synthesis accounted for the majority of acetate carbon accumulated by the conceptus in the acid-insoluble pool. At later stages of development, incorporation into lipids constituted a minor pool of acetate carbon. Some acetate carbon was found in the glycogen fraction of the conceptus. The rate of incorporation into the acid-soluble glycogen fraction by embryos was constant throughout the period studied. By contrast, trophoblast increased its rate of incorporation markedly into both acid-soluble and acid-insoluble glycogen pools as did the yolk sac from Day 17.(ABSTRACT TRUNCATED AT 250 WORDS)