The metabolism of glutamine by the preimplantation sheep conceptus and its interaction with glucose

Abstract

The metabolism of glutamine and glucose, separately and in combination, by the sheep conceptus recovered on Days 2, 6, 13, 15, 17, and 19 of pregnancy was assessed over 2.5 h. At Day 2, the production of CO2 from glutamine was similar to that from glucose, with additive effects seen when both substrates were present. Between Day 2 and Day 6, there was a three-fold increase in glucose oxidation but no change in the oxidation of glutamine. From Day 13 to Day 19, the oxidation of glutamine was relatively high in embryonic tissue, low in trophoblastic tissue and intermediate in the yolk sac but in all tissues decreased as development progressed. Over this latter period the oxidation of glutamine was reduced to approximately 50% by the addition of glucose to the medium but glucose oxidation was unaffected by the addition of glutamine. At the early stages of development, the incorporation of substrate carbon from glutamine was less than that from glucose but in each case, incorporation into the acid-insoluble macromolecular fraction increased 2-3 times between Day 2 and Day 6. Incorporation of glutamine into the Day-17 and Day-19 conceptus was also measured; embryonic tissue exhibited the highest rate of incorporation and trophoblastic tissue the lowest. Incorporation was lower on Day 19 than on Day 17 and the proportion of carbon isolated in the acid-insoluble fraction represented 20% of the total incorporated. At no time did the addition of glucose to the medium alter incorporation of glutamine into either embryonic tissue or extraembryonic membranes.