Can someone help me with a secondary messenger question??

[ColumbiaOrtho]

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I am working on bio problems on destroyer and one of the questions asks which hormone will activate adenylyl cyclase to induce ATP-> cyclic AMP reaction. the answer choice are: trypsin, chymotrypsin, epinephrine, thryoxin, and human growth hormone. The correct answer is epinephrine. I was wondering why can epinephrine induce the secondary messenger cascade and thyroxin cannot while they both are amino acid derivatives. Why can epinephrine act like a peptide hormone while thyroxin can't?? Thank you!

 

[FeralisExtremum]

The thyroid hormones (like thyroxine) are lipid soluble and therefore bind to receptors in the nucleus, and don't use secondary messengers like hormones that bind at the membrane receptors.

 

[ColumbiaOrtho]

The thyroid hormones (like thyroxine) are lipid soluble and therefore bind to receptors in the nucleus, and don't use secondary messengers like hormones that bind at the membrane receptors.

So Epinephrine is hydrophilic while thyroid hormones are hydrophobic. Thank you!

 

[FeralisExtremum]

So Epinephrine is hydrophilic while thyroid hormones are hydrophobic. Thank you!

Correct, the catecholamines (epinephrine and norepinephrine) are water soluble, bind receptors on the target tissue, and primarily act via the secondary messenger cAMP.

It can be confusing at first because both the thyroid hormones and the catecholamines are tyrosine derivative hormones, but the difference is a pretty critical one.