The perivascular contractile sheath of human placental stem villi: its isolation and characterization.

Former studies have shown that fetal blood vessels of stem villi in the human placenta are enclosed by sheaths of presumed contractile cells. Efforts to prove the contractility of these sheaths by isometric and biochemical investigations still suffer from the difficulty of differentiating between extravascular and vascular (media) contractile cells. The present study describes a method for the selective dissection of perivascular tissue sheaths in stem villi of approximately 2-4 mm thickness, which contained abundant alpha-actin immunoreactive cells and were free of adherent vascular smooth muscle cells. These extravascular contractile cells are part of the 'fibrous paravascular sheath', which, in placental pathology, is used as an index of maturity. To emphasize the high number of contractile cells and their location within this sheath, we propose the common term perivascular contractile sheath (PVCS). The isolation method offers the possibility of selectively investigating the contractile forces of the PVCS and of obtaining more insight into its functional role.