Experimental diabetes impairs rat embryo development during the preimplantation period

Congenital malformations and early fetal losses are still the main complications of diabetic pregnancy. Whether the diabetic state affects the early embryo development during the preimplantation period is not known. To understand better the early steps of embryo growth, we collected the embryonic structures from the uterine horns of pregnant diabetic rats on day 5 of pregnancy. Diabetes was induced by streptozotocin (50 mg/kg) injection, 7, 14 or 21 days before mating. The morphological analysis revealed a lower rate of blastocysts (72% of all structures) and an increased rate of morulae (19.5%) in diabetic rats, compared to control animals (86.7 and 7.9% respectively). Hence, diabetic rats had fewer blastocysts (5.5 +/- 2.9 per rat) and more morulae (1.5 +/- 1.7) than control animals (7.2 +/- 2.7 and 0.66 +/- 1.2 respectively). Moreover, blastocysts from diabetic rats had fewer nuclei (26.9 +/- 7.3 per blastocyst) than blastocysts from control animals (31 +/- 6.1). In another set of experiments, subdiabetogenic doses of streptozotocin were administered. In rats injected with 25 mg/kg, neither the glycaemia, nor the morphological aspects of the embryos, nor the number of blastocyst nuclei differed from the control animals. In the animals receiving 35 mg/kg, the glycaemia was increased to approximately twice the control group value. However, the embryonic morphology and the nuclei counting of the blastocysts were similar to those of the fully diabetic group injected with 50 mg of streptozotocin. These results show that experimentally induced diabetes, even of a rather mild degree, affects the embryo development during the preimplantation period. The recovered embryos appear less mature and less developed.