Quantitative analysis of the toxicity of human amniotic fluid to cultured rat spinal cord.

It has been proposed that the myelodysplastic components of a myelomeningocele are secondarily damaged as the result of exposure to amniotic fluid, the so-called 'two-hit' hypothesis. The critical time at which this secondary insult might occur has not been clearly defined. The present study addresses this issue by quantitatively assessing the toxic effects of human amniotic fluid of various gestational ages upon organotypic cultures of rat spinal cord. Using an assay for lactate dehydrogenase efflux to evaluate toxicity in such spinal cord cultures, we found that the amniotic fluid became toxic at approximately 34 weeks' gestation. This toxic effect of amniotic fluid appears to emerge rather suddenly. Accordingly, it seems reasonable to suggest that prevention of exposure of vulnerable spinal cord tissue to this toxicity by surgical closure of a myelomeningocele defect prior to the emergence of toxicity in amniotic fluid may prevent injury to vulnerable myelodysplastic spinal cord tissue.