'De‐watering' capabilities of surfactants in human amniotic fluid.

Abstract

The phospholipid extracts from each of eleven samples of human amniotic fluid obtained from eleven full‐term births were deposited as orientated monolayers adsorbed to glass. The surfaces were found to be rendered hydrophobic with maximum contact angles averaging 54.5 degrees while, upon withdrawing fluid, the edge of the saline pool receded to expose dry surface with minimum contact angles averaging 15.4 degrees. The extracts were found to be surface‐active at the liquid‐air interface and there was some indication that direct adsorption to solid surfaces was facilitated by calcium ions. It was found that, in all extracts, a continuous layer of saline adjacent to the adsorbed surface would break up spontaneously to expose dry surface when the thickness was reduced to an average of 764 micron, corresponding to several alveolar diameters. This phenomenon is discussed as a possible means of establishing dry patches on the alveolar membrane, especially in the new‐born after the fetal alveolar wall has been exposed to the same surfactants in much the same physical form as found in amniotic fluid. Surfactant adsorbed directly to the tissue subphase is suggested as a physical basis for the discontinuity of the aqueous hypophase seen in many electron micrographs of the adult alveolus. This 'de‐watering' of the alveolar surface could facilitate gas transfer.

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

“…An alternative approach has been to argue that, in the normal physiological state, it would be more desirable teleologically if there were no bubble to collapse in the first place and, moreover, no liquid lining to impede gas exchange (Hills, 1981(Hills, , 1982. While there is little doubt that a continuous liquid lining occurs in the fetus at birth or in infants with respiratory distress syndrome (r.d.s.)…”

“…Molecular models for the direct adsorption ofthe primary components ofpulmonary surfactant to the alveolar mucosa have been discussed elsewhere (Hills, 1982(Hills, , 1983b while their ability to act as water repellents has been demonstrated in vitro in two modes. First, they can inhibit fluid in deeper structures from exuding onto that surface (Hills, 1982) and, secondly, they can cause fluid already in contact with the surface to move aside, i.e.…”

“…One possibility is that surfactant can be directly adsorbed to the mucosal surface just as it can be adsorbed to non-biological surfaces (Gershfield, 1979;Hills, 1982) and to cutaneous and tracheal epithelium (Hills, 1982;Hills & Barrow, 1979) to render those surfaces hydrophobic and, hence, water repellent. Electron micrographs used to determine the location of surfactant in the alveolus by Gil & Weibel (1969) and Weibel & Gil (1968) show osmium densities as high at the mucosal surface as any seen at the air-aqueous interface of the 'pools'.…”

“…First, they can inhibit fluid in deeper structures from exuding onto that surface (Hills, 1982) and, secondly, they can cause fluid already in contact with the surface to move aside, i.e. 'de-watering', including the ability to cause spontaneous rupture of continuous layers of adjacent fluid to expose dry surface de novo (Hills, 1983 a).…”

“…The vital question is whether they possess this capability when coating the pulmonary membrane and, in turn, whether they are adsorbed to it when present in the physical form in which those surfactants are actually produced in the fetal lung. The phospholipid extracts from amniotic fluid into which those secretions flow have been shown to impart those properties in vitro (Hills, 1983 a) but do they do so in vivo and in the human in particular?…”