Step I Stimulation test for Hypopituitarism

[MudPhud20XX]

So you would do stimulation tests such as giving GnRH to stimulate LH, FSH or TRH to stimulate prolactin and TSH and I get that.

But why would you do insulin infusion to stimulate GH and ACTH? (Kaplan Physiology book says this without any good explanation.) I mean any particular reason you are not using GHRH and CRH, which are normally produced in hypothalamus that would stimulate GH and ACTH respectively?

Many thanks in advance.

 

[mercaptovizadeh]

So you would do stimulation tests such as giving GnRH to stimulate LH, FSH or TRH to stimulate prolactin and TSH and I get that.

But why would you do insulin infusion to stimulate GH and ACTH? (Kaplan Physiology book says this without any good explanation.) I mean any particular reason you are not using GHRH and CRH, which are normally produced in hypothalamus that would stimulate GH and ACTH respectively?

Many thanks in advance.

You can do a variety of tests for GH, such as insulin (which will lead to hypoglycemia and compensatory rise in GH and ACTH to mobilize glucose), glucagon, which can directly stimulate GH, or GHRH + arginine, which directly stimulates GH release. For ACTH, you can use the insulin stim test as for GH, or you can use CRH, directly stimulates ACTH.

Why not use direct stim tests? I am willing to bet it's an issue of history and cost. Insulin is a very routinely prepare hormone for diabetics and readily available. I bet CRH and GHRH are more expensive and their preparation was developed much later than insulin's. But that's just my best guess.

 

[MudPhud20XX]

Thanks a lot merca! That makes sense. I appreciate your help.

 

[mercaptovizadeh]

Thanks a lot merca! That makes sense. I appreciate your help.

You're welcome. Incidentally, on my pediatric endocrine rotation, when a GH deficiency was plausible, they would look at IGF-1 and IGF-BP3 levels first and order a bone age study. After that come the stim tests.

 

[sanj238]

You can do a variety of tests for GH, such as insulin (which will lead to hypoglycemia and compensatory rise in GH and ACTH to mobilize glucose), glucagon, which can directly stimulate GH, or GHRH + arginine, which directly stimulates GH release. For ACTH, you can use the insulin stim test as for GH, or you can use CRH, directly stimulates ACTH.

Why not use direct stim tests? I am willing to bet it's an issue of history and cost. Insulin is a very routinely prepare hormone for diabetics and readily available. I bet CRH and GHRH are more expensive and their preparation was developed much later than insulin's. But that's just my best guess.

Direct stimulatory tests are not utilized due to their pulsatlie nature in activation as well as GH and ACTH activity being modular throughotu the day- the max activation is during daytime and lowest at night leading to misleading interpretation (non standardized)