HIGH AND LOW-MOLECULAR-WEIGHT KININOGEN AND PLASMA PREKALLIKREIN PLASMA KALLIKREIN IN VILLOUS CAPILLARIES OF HUMAN TERM PLACENTA/

This study examined the expression and presence of components of the k allikrein-kinin system in human term placenta. Immunohistochemical stu dies localized H-kininogen and plasma prekallikrein/plasma kallikrein to endothelial cells of placental villous capillaries. In larger place ntal blood vessels and umbilical cord, neither kininogens nor kallikre ins were detected. High (H) and low (L) molecular weight kininogen, pl asma prekallikrein and plasma kallikrein were detected by Western blot analysis in human term placenta and in maternal and fetal blood, wher eas tissue kallikrein was not. Furthermore, mRNA of plasma prekallikre in was detected by reverse transcriptase-polymerase chain reaction (RT -PCR) in placental homogenates, while mRNA of H-kininogen, L-kininogen and tissue kallikrein was not. Because H-kininogen and plasma prekall ikrein circulate in a complexed form, we suggest that endothelial cell s bind kininogen and plasma prekallikrein in which they are secreted b y the fetal liver from fetal blood. The co-localization of kininogen a nd plasma prekallikrein/plasma kallikrein suggests that kinins could b e generated locally in placental capillaries. When released, they may play a role in regulating placental blood flow and transplacental tran sport of substrates and metabolites. (C) 1996 W. B. Saunders Company L td