[Effects of maternal hyperglycemia on fetal growing mechanism]

The aim of this study was to clarify the effects of maternal hyperglycemia on fetal growth in rats. In streptozotocin (STZ)-induced diabetic rats, maternal serum glucose levels during pregnancy were controlled by daily injection of NPH insulin or saline from day 3 to 21 of pregnancy. The body weight, hepatic glycogen content and serum concentrations of insulin and Insulin-like Growth Factor-I (IGF-I) in fetuses from these rats were measured on Day 21 of pregnancy. Fetal body weight positively correlated with maternal mean blood glucose (MBG) during pregnancy in the groups of diabetic mothers whose MBG was less than 220 mg/dl, whereas a negative correlation was observed in the groups whose MBG was more than 220 mg/dl. In addition, a similar correlation between hepatic glycogen content, serum concentrations of insulin or IGF-I and maternal MBG was observed. On the other hand, in the culture of fetal rat hepatocytes, glycogen content indicated a dose-related increase according to the increase in glucose concentration in the medium. These results suggest that the growth retardation observed in rats whose maternal mean glucose level is higher than 220 mg/dl is not caused by abnormalities in the metabolic function of the fetal metabolic organ (liver), but it is caused by a decrease in the production and/or secretion of growth-promoting factors (for example insulin and IGF-I) in the fetuses.