Final answer:
Drugs categorized as phosphodiesterase inhibitors tend to enhance second messenger systems by increasing the levels of cyclic AMP (cAMP).
Step-by-step explanation:
Drugs categorized as phosphodiesterase inhibitors tend to enhance second messenger systems. Phosphodiesterase (PDE) is an enzyme that deactivates and degrades cyclic AMP (cAMP), which is a second messenger involved in cell signaling. By inhibiting PDE, these drugs increase the levels of cAMP, leading to enhanced signaling and cellular responses.