Glucagon during fasting

Together these three enzymes degrade the original molecule to glycerol and three unesterified fatty acids. In adipose tissue, the primary hormonal effects are mediated by epinephrine in stress situations and by glucagon during fasting. 

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. 

The first phosphatase step is very important FBPase converts fructose,1-6-bisphos-phate into fructose-6-phosphate under allosteric control of several factors but during fasting, glucagon-induced regulation is crucial. One effect of glucagon stimulation of liver cells is to reduce the concentration of fructose-2,6-bisphosphate, an isomer that activates PFK-1 and is itself synthesized by PFK-2 when fructose-6-phosphate concentration rises... 

Induction of enzyme synthesis Glucagon increases the tran scription of the PEP carboxykinase gene, thereby increasing the availability of this enzyme s activity as levels of its substrate rise during fasting. [Note Insulin causes decreased transcription of the mRNA for this enzyme.]... 

Liver glycogen is used to maintain blood glucose during fasting or exercise. -Its breakdown is stimulated by glucagon and by epinephrine via a... 

Glucagon rises during fasting and causes the activation of hormone-sen-... 

Glucagon, which is elevated during fasting, stimulates lipolysis. 

Food deprivation results in an increased expression of PPARa which, by itself, is likely to stimulate p-oxidation. The mechanism by which PPARa expression increases during fasting is unknown. However, as previously mentioned, it might involve PGCl activation downstream of glucagon and glucocorticoids (Louet et al., 2002 Yoon et al., 2001) together with low insulin. 

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