Which Type of Hormone Releases Cyclic AMP as a Second

Question

Which type of hormone releases cyclic AMP as a second messenger?  
A) Peptide only
B) Steroid only
C) Protein only
D) Peptide and protein only
E) peptide, steroid, and protein

Accepted Answer

Peptides and proteins are able to release cyclic AMP as a second messenger as they are unable to pass through the cell membrane and therefore require a signaling pathway to reach the cell interior. Steroids are able to diffuse across the cell membrane and directly bind to intracellular receptors without the need for a second messenger.