Delay in pulmonary glycogen degradation in fetuses of streptozotocin diabetic rats

The developmental profile of pulmonary glycogen was investigated in fetuses of rats made diabetic before conception with the injection of 40 mg/kg streptozotocin. Lungs of control litters showed increasing pulmonary glycogen concentration from day 16-20, followed by significant decline by term (= 22 days). In contrast, the diabetic litters, which had pulmonary glycogen concentration equal to controls until day 20, showed significantly higher glycogen values (P less than 0.01) on days 21 and 22, consistent with a delay in glycogen degradation. This coincided with the finding of decreased amounts of fetal pulmonary phosphatidylcholine and disaturated phosphatidylcholine on day 21 of the diabetic gestation (P less than 0.05), but not before that time. Pulmonary glycogen phosphorylase A activity was significantly decreased in the diabetic litters on the final days of gestation, at the same time that the delay in glycogen breakdown became evident. Pulmonary glycogen synthase activity did not differ in the control and diabetic fetuses. The delay in pulmonary glycogen degradation seen in the fetus of the diabetic gestation is thus temporally related to the delay in lung maturation seen in this model and may be secondary to a decrease in the activity of the glycogenolytic enzyme phosphorylase A. Decreased availability of pulmonary glycogen stores for surfactant synthesis may be important in elucidating the mechanism of the delayed pulmonic maturation seen in fetuses of diabetic pregnancies.