The uptake of amino acids and oxygen across the rabbit uterus in normal and postterm pregnancies

Nineteen pregnant rabbits were studied at three different gestational ages in terms of uterine uptake of amino acids and oxygen under unstressed, steady-state conditions. The three gestational age groups were: (1) 23-25 days, (2) 26-31 days, and (3) 32-34 days (post term). The arteriovenous differences for all amino acids except glutamate and aspartate were significant in groups 1 and 2. Uterine amino acid coefficients of extraction were markedly reduced in the postterm animals (3), despite an increased uterine coefficient of extraction for oxygen. The uterine coefficients of extraction of amino acids were 2-2.5 times greater than those across the pregnant Uterus of the sheep. There was also an increased uptake of amino acid per millimoles/liter of oxygen in the rabbit compared to the sheep. Maternal arterial amino acid concentrations were not significantly different in groups 1 and 2, but the gluconeogenic amino acids serine and alanine were significantly increased in maternal arterial blood of postterm animals.