INTERACTION OF SEX-HORMONES AND CHOLESTEROL WITH MONOLAYERS OF DIPALMITOYLPHOSPHATIDYLCHOLINE IN DIFFERENT PHASE STATE

Interactions of estradiol, progesterone, testosterone and cholesterol with dipalmitoylphosphatidylcholine (DPPC) monolayers at the air/water interface using Wilhelmy-Tensiometer were studied by measuring the ch ange of the monolayer surface tension gamma (mN/m). In order to estima te the role of DPPC phase state on the Delta gamma effects the experim ents were carried out at three temperatures: 37 degrees C, 41.5 degree s C and 47 degrees C, since at 37 degrees C and 47 degrees C the forma tion of ripple gel P-beta and Liquid-crystalline L-alpha DPPC phases r espectively were realized. Surface tension lowering capacity of the in dividual components at the air/water interface decreases in the order cholesterol> estradiol>progesterone>testosterone. The surface tension decrease of previously formed DPPC monolayer alter addition of cholest erol and hormones follows the order cholesterol much greater than estr adiol>progesterone congruent to testosterone. The higher activity of c holesterol and estradiol is interpreted by the existence of hydroxyl g roup in the steroid A-ring and hydrocarbon chain in the cholesterol st ructure and the same hydroxyl group in the estradiol, with possible fo rmation of hydrogen bond between this group and the C=O group of the D PPC. It is shown that the existence of C-H chain in the molecular stru cture is stronger determinant than the OH group regarding the interact ions with the DPPC monolayers. The very low capacity of progesterone a nd testosterone to interact with the DPPC monolayer is explained by th e lack of the C-H chain and OH group in their structures. It was shown that the interaction forces of the steroids studied with DPPC monolay ers were dependent on the DPPC phase state, being in any conditions st ronger in the L-alpha (47 degrees C) than in P-beta (37 degrees C) pha se. At 41.5 degrees C more complex behavior of the components at the m onolayers was observed. The obtained results could serve the concept o f regulated entry of the steroid sex hormones into the cells with the participation of the lipid membrane components. (C) 1998 Elsevier Scie nce Ltd, All rights reserved.