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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