The in vitro effects of insulin on human placental glycogen, glycogen synthetase and glycogen phosphorylase have been studied in fresh immature (10–20 weeks) and term human placental villi. Using an organ culture system, insulin supplementation to the culture medium evoked a glycogenic response in placental tissue in terms of an activation of the glycogen synthetase enzyme system (shift from Dependent to Independent form) and increased glycogen synthesis. The stimulation of placental glycogen synthesis by insulin was consistent irrespective of the glucose concentration, suggesting a direct effect at the level of the glycogen metabolizing enzymes. Results are discussed in light of the mechanisms of action of insulin on glycogenesis in pregnancy.
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