However, with that said it is important to note that insulin is secondary to the glycogen stores available in the muscle and that is where the muscle get its primary energy supply during fight or flight. The higher glucose blood level is for the the other organs, primarily the brain that DOES NOT need insulin to absorb glucose. The brain is ALWAYS number one in allocating available glucose.
OK I've been doing a lot of reading since this topic has been bugging me. In fight/flight, insulin is down-regulated via epi. but glucose is still able to enter the brain because it contains the GLUT2 receptor. GLUT2 is a passive transmembrane protein that passively shuttles glucose, its found in the liver and also in the hypothalamus/cerebrum AKA no insulin required for glucose to enter this cell as you said. Keep in mind though, that glucose cannot cross the blood-brain barrier by itself as your last two sentences imply, the GLUT2 allows glucose into the brain when insulin is not present. This itself answered my big question; why the heck would the body would increase blood glucose levels yet at the same time inhibit/ down-regulate insulin.
Its true that the brain requires nearly twice as much glucose as any other organ since A) it cant store its own glycogen and b) it is constantly metabolically active, especially during fight/flight. However, I dont know if your claims about insulin being secondary in mucsle to glycogen are necessarily true. You are right that muscle muscle glycogen is the primary source of ATP for the cell, but what happens when the glycogen stores are depleted? Note that the liver holds nearly 90% of the glycogen in the body, so muscles do not have enough glycogen for a continued stressful event.
Once the glycogen in the muscle has depleted in the form of pyruvate, ATP and in the case of an oxygen debt, lactic acid, the muscle MUST use blood glucose or else it will not function. The only way its getting this blood glucose is through insulin. Therefore, at some point, insulin must dominate to deliver glucose to skeletal muscle and vital organs (besides the brain which apparently can function without insulin).
I agree with you about gatorade and electrolytes but you cannot deny that strenuous exercise depletes sugar levels. Have you ever watched the ironman competition or some parts of a marathon? They drink gatorade mid-race to not only replenish electroyltes but the glucose serves as an immediate source of energy for muscle. In fact, i read a paper that said glucose in sports drinks are absorbed into the blood stream almost as quickly as an IV because the glucose is in single-chain carbs. I also know this because i work in a kinesiology lab... Do a VO2 max test and compare your blood glucose before and after. Its much lower, why? When the blood sugar levels drop due to the strenuous exercise, glucagon becomes activated (temporarily inhibiting insulin to prevent hypoglycemia) to break down the carbs and raise blood glucose. Then once again insulin dominates to ensure that the body does not become hyperglycemic and provides tissues with glucose for fuel.
the way I see it in fight or flight, insulin is initially inhibited due to norepi. and epi. and glucagon is expressed. Then, at some point insulin must predominate to shuttle glucose into the muscle because it cannot last on its own supply of glycogen. it needs glucose to function and the only way its going to get it is through insulin, if it does not get an adequate glucose supply you will probably fall right before the end of a marathon or right before youre able to escape that wild saber tooth tiger.
sorry to the OP since the last few posts by me are way off topic! to answer your question, ace. is purely an NT while epi. can act as both. They are only looking for a substance that is a NT, not a neurohormone like Epi. Its a really nitpicky Q&A that probs wont show up on the mcat..