Maternal diabetes in rats. I. Effects on placental growth and protein turnover.

The developmental growth of the rat placenta was investigated between days 14 and 21 of gestation in normal control, gestational-diabetic, established-diabetic, and insulin-maintained-diabetic mothers. While established-diabetic mothers were hyperglycemic for 2 wk before and throughout the pregnancy, gestational-diabetic mothers were only hyperglycemic for the second half of pregnancy. Daily insulin replacements successfully restored normoglycemia. The wet weight and protein content of control placentas increased linearly between days 14 and 21. Although placentas from diabetic animals were initially smaller, placentomegaly was found at full term. Placental glycogen concentrations were also markedly increased in all diabetic animals. These changes were largely prevented by insulin replacement. The changes in placental size during normal development and in association with the diabetic state were explained by measuring placental rates of protein turnover (in vivo). In normal placentas, protein synthetic and degradative rates progressively declined over the last week of gestation. Because synthesis rates were unchanged in placentas of diabetic mothers, it appears that the differences in placental size primarily arise from alterations in protein degradation.