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In developmental toxicology adverse effects of chemical substances on fetuses during in utero development are investigated. One important manifestation of such adverse effects are changes in skeletal development during organogenesis, which are generally called anomalies. During risk assessment of anomaly-inducing substances the classification of the findings into variation or malformation is crucial for their categorization as potential reproductive toxicant. While a variation is characterized by a delay in development a malformation represents a permanent irreversible impairment which can affect postnatal survival or health. However, postnatal permanence cannot be assessed in routine studies on developmental toxicity as sacrifice and evaluation of fetuses are carried out one day before their calculated delivery. Furthermore, in part of the skeletal system, especially in the cervical column, development is completed postnatally. Few publications exist that address the topic of postnatal effects of substances. For the past three decades experts have emphasized the need for studies on postnatal consequences of fetal anomalies in order to reduce uncertainties regarding their classification. The aim of the present investigation is to contribute to clarification of the postnatal fate of skeletal anomalies in the vertebral column. For that purpose already processed skeletons of rat fetuses and offspring from earlier experiments with the substance 5-fluoro-20-deoxyuridine (FUDR) were assessed. FUDR is known to induce teratological effects and is frequently used as model substance in teratological studies. Dams in the treatment groups received a single subcutaneous dose of 35, 40, 45, 50, 55, 65 and 75 mg FUDR/kg body weight (bw) on day 11 of gestation. The control group was treated with the vehicle aqua dest. at a volume of 10 ml/kg bw. Offspring were sacrificed on gestational day 21 and on postnatal days 7 and 21. Subsequently animals were subject to the double-staining procedure with alcian blue and alizarin red. Evaluation of the skeletons was carried out with 4-fold magnification under a binocular microscope. All findings were assigned according to the updated internationally harmonized terminology. Based on the results obtained postnatally
recommendation for classification of several anomalies were elaborated in the present study. We recommend the classification of the anomalies vertebra centrum unossified, vertebra centrum asymmetric ossification, vertebra centrum bipartite ossification, vertebra centrum hemicentric (with the exception of cervical vertebrae) as well as vertebra centrum misshapen (with the exception of lumbar vertebrae) as variations. The anomaly vertebra centrum dumbbell-shaped should be classified as malformation based on ist postnatal persistence. The same applies to the anomaly lumbar centrum supernumerary sinister/dexter/sinister+dexter which should also be classified as malformation. The present study contributes to the reduction in uncertainty when it comes to the classification of skeletal anomalies in the vertebral column. Furthermore, it can be concluded from the results of the present study that the consideration of postnatal investigations on the developmental toxicity of substances can contribute markedly to the decrease of risk for human health.