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The Cahill cycle, also known as the alanine cycle or glucose-alanine cycle, [1] is the series of reactions in which amino groups and carbons from muscle are transported to the liver. [2] It is quite similar to the Cori cycle in the cycling of nutrients between skeletal muscle and the liver. [ 1 ]
Cori cycle. The Cori cycle (also known as the lactic acid cycle), named after its discoverers, Carl Ferdinand Cori and Gerty Cori, [1] is a metabolic pathway in which lactate, produced by anaerobic glycolysis in muscles, is transported to the liver and converted to glucose, which then returns to the muscles and is cyclically metabolized back to lactate.
Glutamate in the liver enters mitochondria and is broken down by glutamate dehydrogenase into α-ketoglutarate and ammonium, which in turn participates in the urea cycle to form urea which is excreted through the kidneys. [23] The glucose–alanine cycle enables pyruvate and glutamate to be removed from muscle and safely transported to the liver.
As an example, consider alanine. Alanine is a glucogenic amino acid that the liver's gluconeogenesis process can use to produce glucose. Muscle cells break down their protein when their blood glucose levels fall, which happens during fasting or periods of intense exercise. The breakdown process releases alanine, which is then transferred to the ...
In similar manner, in muscles the use of pyruvate for transamination gives alanine, which is carried by the bloodstream to the liver (the overall reaction being termed glucose-alanine cycle). Here other transaminases regenerate pyruvate, which provides a valuable precursor for gluconeogenesis.
The anti-diabetic drug metformin reduces blood glucose primarily through inhibition of gluconeogenesis, overcoming the failure of insulin to inhibit gluconeogenesis due to insulin resistance. [32] Studies have shown that the absence of hepatic glucose production has no major effect on the control of fasting plasma glucose concentration.
The two organs most commonly affected are the liver and the skeletal muscle. Glycogen storage diseases that affect the liver typically cause hepatomegaly and hypoglycemia; those that affect skeletal muscle cause exercise intolerance, progressive weakness and cramping. [1] Glucose-6-phosphate isomerase deficiency affects step 2 of glycolysis.
Failure in the regulation of glyceroneogenesis may lead to type 2 diabetes, a metabolic disorder that results in high levels of blood glucose and blood lipid. [5] Type 2 diabetes, in addition to a decreased sensitivity to insulin , is associated with the overproduction of triglycerides in the liver, due to excessively active glyceroneogenesis ...