Interaction of hydrocortisone with model membranes containing phospholipid and cholesterol.

Pure and mixed monolayers of lecithin and cholesterol were spread on substrates of dissolved hydrocortisone at 25 and 37 degrees. The presence of hydrocortisone increased the surface pressure of dipalmitoyl and egg lecithin films that were in head contact. The increase in surface pressure was dependent on steroid concentration. There were no significant interactions with coherent cholesterol monolayers. Penetration of hydrocortisone was decreased by the addition of cholesterol to the monolayer system. These model membrane systems indicate that hydrocortisone interacts with the hydrated polar head group of the phospholipid and not with films whose molecules are in hydrocarbon tail contact.