Environmental heat stress effects in the hamster.

Exposure of Syrian hamsters for two twenty-minute periods at 40 degrees C on a single day of pregnancy (ranging from day 6 to day 13) resulted in differing teratogenic effects. Maximum resorption (52.6%) was seen with treatment on day 7 whereas the highest rate of malformation (51.9%) was observed with treatment on day 9. Cranial defects predominated with treatment early in pregnancy (highest incidence of day 9) while limb defects were not observed with any treatment administered before day 9. Exencephaly occurred with treatments on day 6 and 8, with a single case after treatment on day 10. Cleft lip and cleft palate were observed with treatment on days 9 and 10. These studies illustrate the usefulness of the Syrian hamsters in teratological studies and characterize some of effects exerted after mild heat treatment at varying stages of pregnancy.