Administration of a dose of 45 mg streptozotocin/kg on day 2 of gestation produced a diabetic state in pregnant rats and was associated with fetal hyperinsulinaemia. Although there was no evidence of fetal macrosomia, the ratio of fetal liver and lung weight to body weight was greater in fetuses of diabetic rats, suggesting an increase in the size of these organs relative to the body weight.
Maternal and fetal plasma corticosterone levels of diabetic rats between 19 and 22 days of gestation was significantly lower than the corresponding control values. Maternal plasma progesterone levels of diabetic rats were lower than controls on days 19 and 20 of gestation, but higher than controls on day 21 of gestation. The absence of pregnancy-related changes in maternal and fetal plasma corticosterone levels and maternal progesterone levels in diabetic rats suggest that adrenocortical function as well as ovarian and/or placental function may be impaired, which may in turn be related to the observed delay in parturition of approximately 18 h as well as to the low survival rate of the pups.
There was a small increase in the cytoplasmic glucocorticoid receptor concentration in the lung but not in the liver of fetuses of diabetic mothers when compared with fetuses of controls, suggesting that the increased receptor concentration may be a compensatory mechanism to overcome the effect of decreased corticosterone levels and increased insulin levels in the fetuses of diabetic rats.