Tissue distribution of placental leucine aminopeptidase/oxytocinase during mouse pregnancy

Placental leucine aminopeptidase (P-LAP), also called oxytocinase, is an enzyme responsible for hydrolyzing oxytocin. This enzyme is identical to cystine aminopeptidase. We examined the tissue distribution of P-LAP in normal adult mice and also in mothers and fetuses during mouse pregnancy using immunohistochemical (IHC) analysis. P-LAP-immunoreactive protein was expressed in various organs in a cell- and gestational stage-dependent manner. In the kidney, P-LAP was located in distal and collecting tubules but not in proximal tubules. The islet of Langerhans in the maternal pancreas stained positively for P-LAP in the periphery in early gestation. This staining pattern changed so that both the periphery and inner cells were positive during mid-gestation and finally only inner cells were positive in late gestation. Among the hematopoietic cells in the fetal liver, only megakaryocytes showed strong expression of P-LAP. The staining intensity increased with gestation on the apical surface of trophoblasts in the placental labyrinth. These data demonstrate that P-LAP is present in a variety of tissues, and its presence is affected by pregnancy and fetal development. Therefore, P-LAP may play a significant role in various physiological processes in non-pregnant, pregnant, and fetal mice.