The effects of hypoxia on placental glycogen metabolism

The effects of hypoxia on human placental glycogen content and the activity levels of the glycogen-metabolizing enzymes, glycogen synthetase and glycogen phosphorylase, have been determined in fresh term and immature human placental villi and in explants maintained in an organ culture system. Glycogen synthetase activity, rate limiting to glycogen synthesis, decreases during gestation. Phosphorylase activity, catalyzing glycogen breakdown, however, was found elevated in term placental tissue. These findings are consistent with the higher glycogen concentrations present in the immature placenta. Moderate (6 per cent oxygen) and severe (1 per cent oxygen) hypoxia caused extensive glycogenolysis in both term and immature placental villi with a significant increase in the active/inactive phosphorylase enzyme ratio. Moderate hypoxia had little effect on the synthetase enzyme of term placenta but resulted in a substantial (50 per cent) decrease in the glucose-6-phosphate-dependent form of synthetase in the immature placenta. Severe hypoxia caused marked decreases in both placental synthetase and phosphorylase enzyme systems throughout gestation. These studies suggest that control of placental glycogen metabolism during oxygen deprivation may be similar to that of muscle with adenosine 5′-phosphate and glycogen itself playing important roles.