Changes in adrenocortical lipid fluidity of hyperfunctioning human adrenals

Lipid droplets, the storage places of cholesterol in adrenocortical cells, exhibit a relatively uniform appearance studied by the electron microscope but they are heterogeneous in respect of their optical polarizing properties. Optical birefringency was studied in cryosections of normal and hyperfunctioning adrenal cortex by a polarizing microscope, equipped with a cold/hot stage working in the temperature range from −40 to 40°C. The majority of lipid droplets in normal adrenal cortex were optically anisotropic in each cortical zone at room temperature (22°C) indicating a long-range molecular order of the lipid components. The lipids of the zona glomerulosa, in the cases of Conn's and Bartter's syndromes, became anisotropic when the temperature was lowered below ambient. The birefringency of the lipids of the zona fasciculata in the case of Cushing's disease was observed at temperatures below −10°C indicating ordered packing of the components of lipid droplets at this temperature. Thus the lipids were more fluid in the hyperfunctioning, hormone-producing cells—this may represent an optimal precondition for their mobilization and processing by the hydrolyzing enzyme system. The changes in fluidity of the intracellular lipids can be attributed to different functional states in the adrenal cortex. Study of the thermotropic phase transitions of the lipid droplets by polarizing microscopy may be a useful additional method for the diagnosis of some adrenocortical diseases.