Isozymes of lactate dehydrogenase in fetal rat liver. Their correlation with blood oxygen concentrations

The percentages of lactate dehydrogenase (EC 1.1.1.27) isozyme 4 (LDH4) was twice that of LDH5 in fetal rat liver on day 17 of gestation. The proportion of LDH5 and LDH4 reached approximately the same percentage (46% of each) on days 17-20 of gestation. On day 21, the percentage of LDH4 increased sharply at the expense of LDH5. Fetal blood oxygen concentrations increased on day 21 of gestation, but decreased later near parturition. Positive and negative linear correlations occurred during late gestation between concentrations of blood oxygen and LDH4 and LDH5 activities, respectively. These results suggest that the proportion of LDH5 and LDH4 in fetal rat liver may vary according to the amount of oxygen available to the tissue.