Dynamic lipid changes in rapidly proliferating hepatic smooth endoplasmic reticulum during acute dexamethasone treatment of adrenalectomized rats |
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Authors: | Caroline Tobia Holloway Ronald N Margolis |
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Affiliation: | (1) Department of Biochemistry, University of Virginia, 22908 Charlottesville, VA;(2) Department of Internal Medicine, University of Virginia, 22908 Charlottesville, VA |
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Abstract: | The regulation by the cell of subcellular membrane components is dependent on a highly complex balance of nutritional, hormonal
and metabolic events. We have characterized the lipid components of the endoplasmic reticulum (ER) of the liver of adrenalectomized
(ADX) rats and the response of these membrane components to glucocorticoid administration. Membrane microviscosity as measured
by fluorescence depolarization of 1,6-diphenylhexatriene (DPH) was measured and correlated with lipid composition and content
of the membranes. In the ADX rat, a significant increase in membrane microviscosity of the smooth endoplasmic reticulum (SER)
was observed and this was accompanied by an increase in the cholesterol content/mg protein and a decrease in the phospholipid
content/mg protein. A change in the fatty acyl chain composition is observed with a significant increase in the mole percentage
of arachidonic acid (20∶4) and an accompanying decrease in saturated fatty acids. Within 2–6 hr of dexamethasone administration,
a decrease in membrane microviscosity is observed that returns this value to one similar to that for normal control animals.
Both the cholesterol and the phospholipid contents/mg protein are likewise restored to levels similar to that for control
animals beginning at the 2-hr time point. The arachidonic acid and saturated fatty acid content of the constituent phospholipids
do not begin to return to values similar to those for control animals until 6 hr after dexamethasone administration. From
these experiments, we can conclude that glucocorticoids play a significant regulatory role in determining the lipid properties
of rat hepatic microsomal membranes. |
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