Fatty acid metabolism epinephrine

Figure 25-7. Metabolism of adipose tissue. Hormone-sensitive lipase is activated by ACTH, TSH, glucagon, epinephrine, norepinephrine, and vasopressin and inhibited by insulin, prostaglandin E, and nicotinic acid. Details of the formation of glycerol 3-phosphate from intermediates of glycolysis are shown in Figure 24-2. (PPP, pentose phosphate pathway TG, triacylglycerol FFA, free fatty acids VLDL, very low density lipoprotein.)...

The regulation of fat metabolism is relatively simple. During fasting, the rising glucagon levels inactivate fatty acid synthesis at the level of acetyl-CoA carboxylase and induce the lipolysis of triglycerides in the adipose tissue by stimulation of a hormone-sensitive lipase. This hormone-sensitive lipase is activated by glucagon and epinephrine (via a cAMP mechanism). This releases fatty acids into the blood. These are transported to the various tissues, where they are used. 

Norephedrine and ephedrine mimic and stimulate the release of the adrenal hormones norepinephrine and epinephrine. Norephinephrine raises heart rate and epinephrine stimulates carbohydrate metabolism resulting in an increased metabolic rate, fatty acids release from lipocytes (fat cells), and a protein sparing effect. Caffeine simply prolongs the effect. 

Epinephrine Is particularly Important In mediating the body s response to stress, such as fright or heavy exercise, when all tissues have an Increased need to catabolize glucose and fatty acids to produce ATP. These principal metabolic fuels can be supplied to the blood In seconds by the rapid breakdown of glycogen to glucose In the liver (glycogenolysis) and of tri-acylglycerols to fatty acids In adipose cells (lipolysis). 

Epinephrine and the muscle. The action of epinephrine and increased fatty-acid availability on muscle metabolism is shown above. Epinephrine works at both al receptors to increase cytosolic Ca2+, which is needed for contractions, and the b receptor to increase cAMP. The increased cAMP leads to glycogenolysis and a more rapid glycolysis for anaerobic energy. The reactions increased by epinephrine are indicated by purple arrows (see text for more detail). 

The old advantages of epinephrine may be a disadvantage in modem western culture, and be a link between stress or coronary heart disease. In modem-day stress, when epinephrine is released, it is usually not a case of fight-or-flight, but more a problem of meeting deadlines or mental pressures. Thus, the released epinephrine causes the metabolic aspects previously described. The release of fatty acids from the adipose may be particularly detrimental. 

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