Delayed fetal development in two models of disturbed pregnancy of rats. Effect on mortality, body mass development, blood urea nitrogen (BUN) and urinary ammonium concentrations during the first week of extrauterine life.

To induce pregnancy disturbance, two models were used ("endotoxin-model" and "stress-model"), both causing decreased fetal body mass. Fetuses were delivered by Caesarean section in the morning of the 21st gestational day. Postnatal mortality rate during rearing for one week amounted to 12% in controls and was enhanced in the endotoxin- and stress-models (to approximately 25% and approximately 30%, respectively). During this period body mass gain of surviving pups was significantly delayed in the stress-model (approximately 140% of birth mass), compared with controls or pups of the endotoxin-model (160% and 155%, respectively). Additionally, decreased BUN concentrations were registered in newborns as well as 7-day-old pups of the stress-model. Urinary ammonium concentrations were not changed significantly. Possible alterations of metabolic processes in pups of the stress-model are discussed.