The nature of the lactate dehydrogenase isoenzymes in human placenta and related tissues

Abstract

Homogenates of fresh human placenta contain all five lactate dehydrogenase (LDH) isoenzymes. Examination of homogenates of washed slices of placenta suggests that LDH 4 and LDH 5 are the most representative isoenzymes and that the presence of LDH 1, LDH 2 and LDH 3 is due, at least in part, to contamination with blood. Total serum LDH was above 200 U/1 in 6 out of 24 patients in labour; in 5 of these the levels of LDH 4 and LDH 5 were elevated. It is suggested that these isoenzymes come from the placenta. Serum LDH 1 is significantly elevated in pregnancy; toxaemia of pregnancy causes no specific changes. The elevated levels of LDH in cord serum are mainly due to increases in isoenzymes 2, 3 and 4. Foetal and maternal red cells contain predominantly LDH 1, LDH 2 and LDH 3; myometrium and decidua contain predominantly LDH 2, LDH 3 and LDH 4.