Glycogenolysis epinephrine stimulation

Epinephrine stimulates glycogenolysis in skeletal muscle, whereas glucagon does not because of absence of its receptors. 

F-2,6-BE Thus, F-2,6-BP levels are decreased and phosphofructokinase activity is decreased. In liver and muscle, F-2,6-BP is the major allosteric activator of phosphofructokinase. In skeletal muscle, however, the kinase responsible for the synthesis of F-2,6-BP is activated, not inhibited, by cyclic AME Thus, muscle sees an increase in glycolysis following epinephrine stimulation, while the liver experiences a decrease in glycolytic activity. In both tissues, glycogen phosphorylase is activated and glycogenolysis occurs. Under these conditions, glucose is utilized in muscle for ATP production relative to contractile activity, while the liver produces glucose for export to the blood. 

Epinephrine stimulation of lipolysis in adipocytes is thought to differ from epinephrine stimulation of glycogenolysis in the liver in which way ... 

Future work will be needed before a complete understanding of how insulin reverses glucagon/epinephrine stimulation of glycogenolysis is obtained. 

In addition to the study of glycogenolysis, a classical example of the mediation of hormone action by cAMP, other studies include epinephrine stimulation of heart contraction and the induction of lipolysis by a variety of hormones. Epinephrine stimulates cardiac contraction almost instantaneously, the stimulation is inhibited by adrenergic blocking agents, and cAMP mimics the effect of epinephrine. When epinephrine is added to the isolated heart, the levels of cAMP are considerably increased within minutes, and when contraction is blocked, the levels of cAMP are reduced in proportion to the effectiveness of the blocking agent. 

Isoproterenol is the most potent stimulant of skeletal muscle glycogenolysis, followed by epinephrine and norepinephrine. (3z-Adrenoceptors mediate muscle glycogenolysis. Stimulation of skeletal muscle glycogenolysis will raise blood lactic acid levels rather than blood glucose levels because skeletal muscle lacks the enzyme glucose-6-phosphatase, which catalyzes the conversion of glucose-6-phosphate to glucose. 

Activation of Gs or Gi proteins results in stimulation or inhibition, respectively, of adenylyl cyclase which catalyses the formation of cyclic adenosine monophosphate (cAMP) from ATP The cAMP binds to protein kinase A (PKA), which mediates the diverse cellular effects of cAMP by phosphorylating substrate enzymes, thereby increasing their activity. Among the responses mediated by cAMP are increases in contraction of cardiac and skeletal muscle and glycogenolysis in the liver by adrenaline (epinephrine). Because a single activated receptor can cause the conversion of up to 100 inactive Gs proteins to the active form, and each of these results in the synthesis of several hundred cAMP molecules, there is a very considerable signal amplification. For example, adrenaline concentrations as low as 10-10 M can stimulate the release of glucose sufficient to increase... 

Circulating catecholamines such as epinephrine also result in an intracellular movement of potassium by two mechanisms. They stimulate the /S-receptor, which directly activates the Na" " -K" " -ATPase pump. Secondly, they stimulate glycogenolysis, which raises blood glucose levels, thereby increasing insulin secretion. This dual mechanism is often used therapeutically in patients with hyperkalemia to normalize serum potassium concentrations. 

Binding of epinephrine to the (3-adrenergic receptors in heart muscle stimulates glycogenolysis and enhances the rate of muscle contraction. Prolonged treatment with epinephrine, however. Induces proliferation of these cardiac muscle cells. In extreme cases, such cardiac by pertrophy causes failure of the heart muscle, a major cause of heart disease. This eplnephrlne-lnduced cell proliferation results... 

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