So for some reason, i'm having difficulty understanding this concept. In growth hormone excess (such as acromegaly), you have an increase in IGF, which apparantly causes hyperglycemia. I don't understand how an excess of IGF causes hyperglycemia, if IGF's function is similar to that of insulin. shouldn't it cause hypoglycemia?
First of all, this is a great question.. a lot of times when people post questions I want to answer: did you look at the FA index before posting this.
But clearly, this is a difficult concept and one worth discussing.
So first of all, lets distinguish the fact that there are two IGF's, IGF-1 and IGF-2.. in this case you are referring to IGF-1 (aka somatomedin).
What happens normally is GH stimulates the liver to produce IGF-1 and IGF-1 directly causes growth in peripheral tissue/organs. In acromegaly, the cause is usually a GH producing tumor which in turn causes a spike increase in IGF-1 levels without feedback inhibition (see picture, GH never takes a break).
http://en.wikipedia.org/wiki/File:Acromegaly_growth_hormone_levels.JPEG
The Hyperglycemia you are referring to is a late stage effect of acromegaly because like in overproduction of insulin, you get receptor desensitization and thus, you are right, it does act like insulin.. Think about it.. in an obese person, so much insulin eventually leads to diabetes mellitus and thus hyperglycemia right?
BTW< i hope someone else comes in and confirms this.. I am going off top of my head, but I think this makes sense. Thanks for the great question otacon, u really made me have to think for a change.
