Dexamethasone-induced alterations in lipid composition and fluidity of rat proximal-small-intestinal brush-border membranes.

A series of experiments were conducted to examine the possible effects of subcutaneous administration of the synthetic glucocorticoid dexamethasone (100 micrograms/day per 100 g body wt.) on the lipid fluidity and lipid composition of rat proximal-small-intestinal brush-border membranes. After 4 days of treatment, membranes and their liposomes prepared from treated animals possessed a greater fluidity than did their control (diluent, 0.9% NaCl) counterparts, as assessed by steady-state fluorescence-polarization techniques using several different fluorophores. Examination of the effects of temperature on the anisotropy values of 1,6-diphenylhexa-1,3,5-triene, using Arrhenius plots, moreover, revealed that the mean break-point temperatures of the treated preparations were approx. 3-4 degrees C lower than those of their control-preparation counterparts. Changes in the sphingomyelin/phosphatidylcholine (PC) molar ratio as well as in certain of the fatty acids of the PC fraction of treated membranes, secondary to alterations in membrane PC levels and in lysophosphatidylcholine acyltransferase activities respectively, were also noted after dexamethasone administration. These compositional alterations appeared to be responsible, at least in part, for the differences in fluidity noted between treated and control plasma membranes. These results therefore demonstrate that dexamethasone administration can modulate the lipid fluidity and lipid composition of rat proximal-small-intestinal brush-border membranes.