Placental transport and utilization of amino acids and carbohydrates

Uteroplacental tissues have been shown to have a high rate of metabolism under in vivo steady-state conditions. Fully two-thirds of the glucose and one-half of the oxygen consumed by the uterus are utilized by these tissues rather than by the fetus. Its high metabolic rate must be borne in mind in any analysis of tracer kinetics, which prohibits the exclusion of these tissues and the use of a two-compartment model for analysis of carbohydrate and amino acid metabolism. Current techniques permit determination of utilization rates of nutrients in all three compartments (fetal, uteroplacental, and maternal) with considerable precision. Using tracer amino acids one can determine rates of protein synthesis and protein breakdown as well as rates of amino acid oxidation. These techniques should prove useful in investigating the role of various trophic factors in fetal life and in assessing the impact of changes in placental function or maternal nutritional state on fetal growth and metabolism.