Epinephrine & Norepinephrine

[orangeman25]

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So I would say that epinephrine is a hormone while norepinephrine is a neurotransmitter. Both are catecholamines and release of either increases blood glucose.

On a practice test (TBR), I found out that epinephrine stimulates insulin secretion while NE inhibits insulin secretion. But the effect of both is to increase blood glucose? Is there something else going on that I'm not seeing? How is this possible?

 

[sazerac]

While they are both catecholamines, they are different chemicals and activate different receptors. First year medical students are generally taught that epinephrine activates the beta-2 receptor in addition to all the receptors that norepinepherine activates (as usually the details are even more complex...).

Anyway, they both activate the alpha-1 receptor which causes glycogenolysis and gluconeogenesis, which will raise the blood sugar by destroying glycogen and amino acids and stuff. Epinepherine is special and will activate the beta-2 receptor which also raises insulin levels, so the new blood glucose has someplace to go. Apparently the insulin levels are not raised so high as to actually lower the net blood glucose levels. So there really isn't a contradiction here. You can read more about these catecholamines and receptors in wikipedia.

This is probably way beyond the scope of the MCAT - I didn't learn it myself until M2 year - and I'm sure any necessary details would be described in a passage.

 

[phattestlewt]

Additionally, realize that neurotransmitter can have both inhibitory and excitatory effects.

What's more important here is to realize that hormones will cause specific effects, whereas with neurotransmitters (e.g. AcH) you can have either a inhibitory or excitatory response depending on the post-synaptic receptor, so just by virtue of knowing the NT you really don't have much information except that its a molecule that relays an AP.

Hope that makes sense.

I also wouldn't worry to much about this as sazerac mentioned.