Twenty-six out of fifty pregnant rats died on days 18-20 of gestation at 33 degrees C environment. The death generally occurred in the dark period around 1-5 a.m. Shortly prior to the death, very high body temperature of 42.0-43.7 degrees C were recorded and the blood pressure was undetectably low. In autopsy, the finding in the main was the congestion in lungs and liver. In temporal changes of body temperature and heart rate, influences of hot environment were observed, but there was no significant difference between dead pregnant group and delivered pregnant group at 33 degrees C environment. At 23 degrees C, the blood pressure of pregnant rats starting at about 140 mmHg level, reached 160-168 mmHg on day 12 of gestation and maintained the level to day 16. On day 18, the pressure returned to 140-145 mmHg and unchanged to term. At 33 degrees C, significant differences were obviously observed between dead group and delivered group in temporal changes of blood pressure. The blood pressure of rats delivered sharply increased to 170 mmHg or more in the middle stage of pregnancy and decreased to about 140 mmHg in the final stage. However, these of dead group increased to 160 mmHg or less in the middle stage of pregnancy, and maintained the level until the final stage.
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