Metabolic Quotients and Oxygen Extraction across the Uterus of the Post-Term Pregnant Rabbit under Chronic Steady-State Conditions

Abstract

The extraction of oxygen by the uterus in the term rabbit has been found to be very high. During post-term pregnancy, the fetuses of the rabbit are approximately 40% larger, despite a reduction in placental weight of approximately 30%. The purpose of our study was to investigate the changes that occur in the maternal rabbit to allow survival of the fetus under these conditions. Post-term pregnancies were induced in 5 white New Zealand rabbits by injections of chorionic gonadotropin and progesterone on the 26th day of gestation. Catheters were placed surgically on day 28, and blood samples were taken daily from the femoral artery and uterine veins starting at day 31. Each sample was analyzed for pH, PCO₂, PO₂, oxygen capacity and saturation, glucose, β-hydroxybutyrate, lactate and acetoacetate. Coefficients of extraction were calculated for oxygen and metabolic quotients were calculated for each substrate. These data are compared with those obtained for the term rabbit in previous studies. There was a significant increase in the coefficient of oxygen extraction in the post-term animals; however, the metabolic quotients across the uterus were not significantly different between the term and the post-term rabbit.

The Uptake of Amino Acids and Oxygen across the Rabbit Uterus in Normal and Postterm Pregnancies

“…3). These data are consistent with data describing a slower rate of fetal growth in postterm pregnancies and a higher coefficient of extraction of oxygen across the uterus [7,20,21]. Given these observations, it will be of interest to study amino acid catabolism and urea production by the preg nant uterus during the postterm period.…”

“…There were no significant differences in the litter sizes in each horn within the three groups. The increase in fetal weight and re duction in placental weights for postterm animals previously reported [7] was con firmed in these studies ( fig. 1), leading to a significantly greater fetal/placental weight ratio among the postterm animals.…”

“…Studies were started at least 3 days after surgery and only when food intake had returned to normal levels (average daily food intake: 120 g). For the postterm animals, the pregnancy was pro longed by giving 50 mg of progesterone intramuscu larly on day 26 of gestation [7], Animals in group 1 were operated upon between 19 and 22 days gesta tion, those in group 2 between 21 and 27 days gesta tion and the postterm animals were operated upon for catheter placement on day 28 of gestation.…”