Surface activity of prostaglandins E2, F2α, A1, and B1 in presence of insoluble monomolecular films

Abstract

Surface activities of four naturally occurring prostaglandins, PGE2, PGF2α, PGA1, and PGB1, were investigated by examining the π-A compression isotherms obtained for insoluble monomolecular films of stearic acid spread on subphases containing the prostaglandins. All four compounds were observed to bring about increased instability of stearic acid monolayers, as evidenced by reductions in both transition and collapse surface pressures. Prostaglandin E2 did not readily penetrate the monolayer but appeared capable of associating with the polar groups of the film, bringing about monolayer instability. PGB1 exhibited a disruptive effect upon monolayer structure, causing some expansion of the π-A isotherm and increased instability. Prostaglandin F2α penetrated into the stearic acid film, giving rise to increased surface pressure development in the initial regions of the π-A curve, resulting in a significantly expanded isotherm. This same effect, in the case of PGF2α, was observed using cholesterol and distearoyl phosphatidic acid monolayers. PGA1 also appeared to penetrate the stearic acid monolayer, forming a mixed monolayer system and causing considerable rearrangement in monolayer structure as evidenced by an extended plateau region occurring in the π-A plot. The order of surface activities observed for the prostaglandins was PGA1 > PGB1 > PGF2α > PGE2. The relative importance of polar functions, hydrophobic interactions, and hydrogen bonding are discussed with respect to the observed effects on monolayer stability. Some biological implications of the data are presented.