Skeletal malformations in rat offspring. Long-term effect of maternal insulin-induced hypoglycemia during organogenesis.

We studied the effect of maternal hypoglycemia on skeletal growth in the offspring of nondiabetic and diabetic rats. Female Wistar rats were injected with streptozocin (30 mg/kg i.v.) 2-3 wk before mating, and diabetes was confirmed by an intraperitoneal glucose tolerance test. On postconception day 9.5 or 10.5, both control and diabetic dams received saline or Actrapid human insulin (400 mU/rat i.p.). Hypoglycemia (approximately 2.8 mM) was induced for 120 min in the insulin-treated mothers. Pregnancy was terminated on gestational day 20. Fetal bones and cartilage were double-stained with alizarin red S and alcian blue 8GS. Insulin-induced hypoglycemia caused delayed ossification in the fetuses of the control dams. The number of malformations, e.g., costal fusion waves, increased greatly. These effects were more striking in the fetuses of dams that had received insulin on day 10.5 rather than on day 9.5 of embryo development. This type of insulin-induced hypoglycemia further delayed ossification of the fetal bones in diabetic dams. The influence of maternal hypoglycemia on skeletal malformations and/or variations was greater in the fetuses of diabetic dams than in the fetuses of control dams. These data suggest that maternal hypoglycemia in early pregnancy has a striking effect on skeletal growth and malformations in fetuses. In addition, mild glucose intolerance in dams may amplify these hypoglycemic effects.