title: An ultrahistochemical study of the placental content of respiratory enzymes in normal and prolonged pregnancies.
abstract: The placental content of malate dehydrogenase and lactate dehydrogenase has been studied at the ultrastructural level. In the trophoblast both enzymes have a predominantly mitochondrial localization although occasional membrane-bound extra-mitochondrial activity is also seen. As compared with the first trimester placenta, there is a highly significant decrease in the activity of both enzymes within the trophoblast at term; this may represent an adaptative change to reduce placental oxygen consumption and increase the amount of oxygen available to the fetus. In prolonged pregnancies, there is a continued decline in trophoblastic malate dehydrogenase activity but the lactate dehydrogenase activity tends to increase, these changes suggesting that there is a switch from oxidative pohosphorylation to anaerobic glycolysis. It is not clear whether this change to a less efficient mode of energy generation is due to an intrinsic ageing change within the trophoblast or is secondary to placental ischaemia.
mesh_terms: D000818:Animals; D005260:Female; D005865:Gestational Age; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D008291:Malate Dehydrogenase / Q000378:metabolism*; D010920:Placenta / Q000201:enzymology* / Q000648:ultrastructure; D011247:Pregnancy; D011273:Pregnancy, Prolonged; D014327:Trophoblasts / Q000201:enzymology
chemical_list: D007770:L-Lactate Dehydrogenase; D008291:Malate Dehydrogenase