Final answer:
A cAMP inhibitor would prevent the formation of cAMP, leading to the inhibition of protein kinases activation and disruption of the peptide hormone-mediated signaling pathway. This inhibition halts the phosphorylation cascade and the resulting cellular response.
Step-by-step explanation:
The effect of a cAMP inhibitor on a peptide hormone-mediated signaling pathway would be to prevent the activation of protein kinases, which are crucial for propagating the signal initiated by the hormone binding.
When a peptide hormone binds to its receptor on the cell surface, it typically leads to the activation of G-proteins, which in turn activate adenylyl cyclase. Adenylyl cyclase then converts ATP into cAMP, which serves as a second messenger to activate protein kinases.
These kinases trigger a phosphorylation cascade resulting in a cellular response. If a cAMP inhibitor is present, it directly impedes cAMP formation, thereby inhibiting downstream signaling events.
An illustrative example is that of somatostatin, also known as growth hormone-inhibiting hormone (GHIH), whereby binding of this hormone to its receptors decreases the levels of cAMP.
This reduction in cAMP levels leads to the inhibition of human growth hormone secretion. This demonstrates the significance of cAMP in hormone signaling pathways, and how its inhibition can effectively short-circuit the process.
Moreover, enzymes such as phosphodiesterase (PDE) regulate the duration and intensity of the hormone signal by degrading cAMP. Therefore, an inhibitor of cAMP generation would mimic the action of PDE, leading to a decrease in hormone activity.