Size of L-lactate transport from the fetal rat to the mother animal.

U- -14-C-L-lactate injected into the fetal rat in utero during the last period of pregnancy (3 days before birth) could be detected in the maternal circulation. The label in the blood sampled from the uterine vein was present in L-lactate for 90% or more. Determination of the fetal lactate pool, estimation of the total amount of labeled L-lactate transported to the mother animal and the assumption that during the time course of label transport the ratio of integrated amount of 14-C-lactate sampled over the total amount of transported labeled lactate was constant, permitted calculation of the rate of lactate transport. Values of about 275 nmoles/min/g fetal tissue were found. In case of 40 g fetal tissue (10 fetuses 1 day before birth) about 11 mumoles lactate/min must be taken up by the mother. Reoxidation of cytoplasmic NAD+ in fetal rat cells is mainly effectuated by reduction of pyruvate into L-lactate.