Pathological effects of maternal hypoglycemia on fetal development in cats

The pathogenesis of fetal brain damage caused by acute maternal hypoglycemia was investigated experimentally in cats: profound hypoglycemia (blood glucose concentration: less than 30 mg/dl) was induced in 12 pregnant cats at various stages of gestation by intravenous bolus injections of insulin. Maximal hypoglycemia was attained within 2-3 h, although the grade and duration in individual cats varied. The EEGs of all of seven maternal cats examined showed an increased frequency of slow high-voltage waves as hypoglycemia progressed, eventually becoming flat in 3 for a maximum period of 20 min. Some fetuses showed severe neuropathological changes, such as infarction or intrauterine death. Subventricular softening, cortical hemorrhage and ischemic neuronal changes also occurred, being distributed symmetrically in the parasagittal areas of the cerebrum, basal ganglia, thalamus and tegmentum of the brainstem. In general, these pathological changes were more marked in fetuses and neonates than in the maternal cats, in which only ischemic neuronal changes were present, and may have been due to fetal systemic hypotension and cerebral ischemia induced by hypoglycemia. In maternal cats, the distribution of neurons showing ischemic changes was widest in the cerebral cortex, and some were also present in the dentate gyri of the hippocampus. Moreover, ultrastructural examination of the ischemic neurons in maternal cats, unlike those of the fetuses, showed no mitochondrial swelling. Therefore, the distribution and ultrastructural nature of the ischemic neurons found in the maternal cats were considered to be characteristic of hypoglycemia, as proposed by Agardh et al. (1980).