Changes in the offspring of rats exposed to acute hypoxia during pregnancy were investigated in terms of the circadian rhythm of plasma corticosterone contents and brain acetylcholine levels for periods ranging from 15 to 120 postnatal days. The accelerated maturation of the daily adrenocortical rhythm and the retarded maturation of the circadian rhythm of brain acetylcholine levels were observed in the offspring of the maternal animals subjected to acute hypoxia three times. The same offspring, on the other hand, began to show, when as late as 90 to 120 days old, certain changes of the circadian rhythms already formed, which were characterized by the significant decrease in the evening value for corticosterone and also by that in the morning for brain acetylcholine levels as compared with the control groups. The more often the offspring experienced acute hypoxia in the fetal stage, the more markedly the above changes occurred. It was postulated that experimental acute hypoxia imposed on the mother produced certain chemical changes in the brain of offspring.
