Corticosteroid-induced lipid changes in rat liver microsomes.

An influence of corticosteroids on the phospholipid composition of several tissues has been demonstrated previously. Increases in the activity of rat liver microsomal cytochrome c reductase and aryl hydrocarbon hydroxylase after corticoid administration were also demonstrated. The phospholipid composition of liver microsomes is now reported to be altered by similar corticosteroid treatment. Phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin levels in rat liver microsomes were decreased significantly after in vivo cortisol administration. The levels of palmitic, stearic, oleic, linoleic, and arachidonic acids in phosphatidylcholine and of palmitic acid in phosphatidylserine-phosphatidylinositol were also affected. Cholesterol was increased after adrenalectomy and decreased to control levels after the administration of cortisol. Some of the microsomal enzymes which are affected by corticosteroids or adrenalectomy are known to require phospholipids for full activity. The alteration of enzyme activities and membrane phospholipid composition by similar dosage schedules of corticosteroids suggests a possible relation between the two effects. By affecting the lipid composition of the membranes, corticosteroids may regulate or modulate the activity of the lipid-requiring enzyme systems.