Moses, Robyn Marie (2020-07). Utilization of Glucose and Fructose by the Ovine Conceptus During the Peri-Implantation Period of Pregnancy. Master's Thesis.
Thesis
Early embryonic development in the sheep requires elongation of the conceptus (the embryo and associated extraembryonic membranes) before implantation can take place. This requires energy and biomolecules provided by various metabolic pathways, often initiated by glucose as a preferred metabolic substrate. However, the ovine trophectoderm in the conceptus converts glucose from the maternal vasculature to fructose, resulting in a greater abundance of fructose than glucose, especially in fetal plasma and fetal fluids in later stages of pregnancy. The role of fructose is overlooked due to a preference of glucose over fructose. This study investigated the capability of the ovine conceptus during Days 16 and 17 of gestation to metabolize fructose via the tricarboxylic acid (TCA) cycle and pentose phosphate pathway. A study was conducted by culturing Day 17 ovine conceptuses with universally labeled glucose and fructose with combinations of unlabeled glucose and fructose. Results suggested that the conceptus metabolizes both glucose and fructose, indicated by the production of 14CO2, but glucose is the preferred substrate (P<0.05). Immunolocalization of ketohexokinase, which allows fructose to bypass glycolytic regulatory mechanisms, in uncultured conceptuses and endometrium on Days 17, 18, and 30 of pregnancy indicated that ketohexokinase is expressed in the endoderm of the conceptus, as well as the trophectoderm and uterine luminal and glandular epithelium. A second experiment was conducted to investigate the metabolism of glucose and fructose by Day 16 ovine conceptuses via various metabolic pathways. The conceptuses were cultured similarly to that in the first experiment, using specifically labeled glucose and fructose to estimate metabolism via the pentose phosphate pathway and TCA cycle, and homogenized at the end of the experiment to evaluate incorporation of glucose and fructose into lactate, pyruvate, lipids, and glycoproteins. The results indicated that the ovine conceptus could metabolize both glucose and fructose by these pathways, with the exception of lipids, with glucose being the preferred substrate. Contribution of fructose to the TCA cycle were greater than the pentose phosphate pathway when glucose was absent (P<0.05). Results of both studies indicated that the ovine conceptus could metabolize fructose to support conceptus development in the sheep.
