Glycogen content & structure & some enzymes of glycogen metabolism in human foetal organs

The glycogen content, and its structure and the enzymes involved in glycogenolysis in human foetal organs were studied at different periods of gestation. Of all the tissues studied glycogen content was found to be the highest in cardiac muscle. Very little glycogen was present in the foetal liver at 9-12 wk of gestation, this increased progressively to nearly 2 per cent at 24 wk. Glycogen content of placenta was lower than that of skeletal muscle and liver. The level of glycogen in adipose tissue, placenta and cerebrum was not high enough to play any role in glucose homeostasis of the foetus. Human foetal liver and skeletal muscle glycogen showed the normal branched structure while the liver glycogen was found to be unusually stable. Glycogen phosphorylase activity in the foetal liver and muscle was found to be low, i.e., about a fifth and a fourth of adult liver and muscle activity respectively. The stability of foetal liver glycogen and phosphorolytic activity in the liver and muscle indicate negligible glycogenolysis during foetal development. Glucose-6-phosphatase activity in foetal liver was undetectable below 12 wk of gestation, the activity increasing progressively up to 24 wk.