Effects of Cortisol on Fat
Metabolism
Mobilization
of Fatty Acids. In much the same mannerthat cortisol promotes amino acid
mobilization from muscle, it promotes mobilization of fatty acids from adipose
tissue. This increases the concentration of free fatty acids in the plasma,
which also increases their uti-lization for energy. Cortisol also seems to have
a direct effect to enhance the oxidation of fatty acids in the cells.
The mechanism by which cortisol promotes fatty acid mobilization is
not completely understood. However, part of the effect probably results from
diminished transport of glucose into the fat cells. Recall that
a-glycerophosphate, which is derived from glucose, is required for both
deposition and mainte-nance of triglycerides in these cells, and in its absence
the fat cells begin to release fatty acids.
The increased mobilization of fats by cortisol, com-bined with
increased oxidation of fatty acids in the cells, helps shift the metabolic
systems of the cells from utilization of glucose for energy to utilization of
fatty acids in times of starvation or other stresses. This cor-tisol mechanism,
however, requires several hours to become fully developed-not nearly so rapid
or so pow-erful an effect as a similar shift elicited by a decrease in insulin.
Nevertheless, the increased use of fatty acids for metabolic energy is an
important factor for long-term conservation of body glucose and glycogen.
Obesity
Caused by Excess Cortisol. Despite the fact thatcortisol can cause a moderate degree of fatty
acid mobilization from adipose tissue, many people with excess cortisol
secretion develop a peculiar type of obesity, with excess deposition of fat in
the chest and head regions of the body, giving a buffalo-like torso and a
rounded “moon face.” Although the cause is unknown, it has been suggested that
this obesity results from excess stimulation of food intake, with fat being
generated in some tissues of the body more rapidly than it is mobilized and
oxidized.
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