Pulmonary surfactant: hydrophobic nature of the mucosal surface of the human amnion.

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Abstract
The contact angle has been measured for a drop of saline placed upon the rinsed mucosal surface of the amnion in eleven human placental membranes obtained from normal births at full term. The contact angle averaged 70 degrees, indicating a hydrophobic surface comparable with graphite (86 degrees), polyethylene (94 degrees) or oxyntic tissue (85 degrees) which is also exposed to endogenous surface‐active phospholipids in vivo. By comparison, four pre‐term placentas with an average gestation period of 29.5 weeks gave a mean contact angle of 32 degrees, indicating that hydrophobicity of the placenta increases with maturity (41 weeks) and might well be imparted by adsorbed surfactants present in amniotic fluid and known to render other surfaces hydrophobic. Since the mucosal epithelium of the amnion is exposed to the same surfactants in the same physical state as the fetal alveolar wall, the above results imply that this surface may also be hydrophobic, as indicated in the adult lung by other studies. The concept of surfactant directly adsorbed to the pulmonary tissue surfaces is discussed in connexion with its possible functional advantages in 'de‐watering' the lung at birth, maintaining homeostasis by water repellency , releasing airway surfaces and lymph ducts glued by protein and lubricating tissue respiratory movement.