Evidence, evolution and pattern of contractile elements in villous vascular walls and stroma of human placentas of premature infants of different gestational ages. An immuno-morphologic comparative study.

The contractile elements of the human placenta villous tree represent a topic of interest and many issues persist still open. Histology of the stroma and muscular wall and their evolution, in relation with the gestational age, remains to be clarified for a deeper understanding of the adaptive potential and pathogenetic mechanisms. In our study, 56 premature placentas (21-36 wks) were considered, sub-divided into four groups based on age of gestation and compared to 23 at-term placentas (37-40 wks). All cases were tested with anti-smooth muscle actin (SMA) and anti-desmin antibodies to identify the contractile elements in the stroma and in vascular walls of villi. SMA and desmin staining show evident decreased expressions during the pregnancy (temporal variation) and from proximal to distal part of the villous tree (spatial variation) being higher in the stem villi. Both pre-term and at-term placentas showed persisting, although variable, positivity for SMA and desmin staining in the stroma and in the vessel walls of the mature intermediate and terminal villi. This represents an unexpected finding and nothing alike has been previously reported in literature. Both highly premature and term placentas seem to maintain contractile components within each type of villi, represented by both myofibroblasts and mature smooth muscular cells. These components may be present in both villous vascular walls and stroma, albeit with different staining intensity. This finding allows us to imagine an active function in the regulation of the blood flow, not only in stem and intermediate immature villi but even in smaller villi.