Epinehrine vs cortisol effects on metabolism

[BlueCircle]

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How do these two hormones influence metabolism? I read somewhere that epinephrine shifts metabolism from favoring adipose metabolism over carbohydrate (glucose) metabolism. I also read that epinephrine inhibits insulin and activates glucagon, so thereby increasing blood glucose levels. I'm trying to connect the dots here. Does epinephrine do this to basically starve the cells of glucose by "storing" it in the blood and not allowing the cells access to it? Thereby causing the cells to rely on lipid metabolism? And if so then why does epinephrine also promote glycogen breakdown? And what about cortisol?

 

[BlueCircle]

This is the conflicting thing I read about Cortisol in the Kaplan book:

“In order to make a getaway in the “fight-or-flight” response, glucose must be rapidly mobilized from the liver in order to fuel actively contracting muscle cells ”

but later they say:

“cortisol inhibits glucose uptake in most tissues (muscle, lymphoid, and fat) and increases hepatic output of glucose via gluconeogenesis
”

Muscle cells need insulin to uptake glucose, and cortisol acts in opposition to the effects of insulin. I also know that some tissues like nervous tissues, which innervate muscles of course, don't need insulin to take in glucose. But if we we in a flight or fight state, it makes more sense to me to fire up both the nervous system and muscles with glucose. I know skeletal muscles already have their own glucose stores. Is that the missing piece? My thinking was that skeletal muscles can easily burn through their glycogen stores, and would benefit from tapping into the blood glucose store.

 

[aldol16]

Think in terms of why you're making epinephrine in the first place. Epinephrine is a hormone made by the adrenal medulla in response to a "fight-or-flight" stimulus. So what's happening and what does your body want to happen? Your body wants to slow down metabolism in places that are not essential for the sympathetic response while increasing metabolism in tissues that are. So it will redirect glucose from the liver to the muscles - this is why liver GLUT transporters have a higher Km than muscle transporters. Anyway, epinephrine will increase fatty acid breakdown because you want all that energy you can get from oxidative phosphorylation. So all of these effects have the net result of increasing glucose to the muscles so you can fight or hide.

With regard to cortisol, I'm less familiar with that but I believe the timescale of action of cortisol is much slower than epinephrine.

 

[Necr0sis713]

This is the conflicting thing I read about Cortisol in the Kaplan book:



but later they say:



Muscle cells need insulin to uptake glucose, and cortisol acts in opposition to the effects of insulin. I also know that some tissues like nervous tissues, which innervate muscles of course, don't need insulin to take in glucose. But if we we in a flight or fight state, it makes more sense to me to fire up both the nervous system and muscles with glucose. I know skeletal muscles already have their own glucose stores. Is that the missing piece? My thinking was that skeletal muscles can easily burn through their glycogen stores, and would benefit from tapping into the blood glucose store.

Your brain depends on glucose more than any other organ, so in times of stress your liver needs to provide glucose to your brain, which is cortisol's job.

Now, muscle has it's own glycogen that it breaks down when epinephrine acts on it. In fact, your muscle can't release it's glucose into the blood stream like the liver can, because it can't turn G6P back into glucose. Instead, the glycogen gets turned into G6P and then your muscle uses it up for stressful situations.

So...think of your liver as being able to put glucose into your blood, while your muscle CAN'T. The muscle uses it's own glucose from it's own glycogen stores.