What is the role of nitric oxide as a signaling molecule, and how is it synthesized?

• A. Nitric oxide is synthesized from cyclic GMP and causes smooth muscle relaxation.
• B. Nitric oxide is synthesized from arginine and oxygen and causes smooth muscle relaxation.
• C. Nitric oxide is synthesized from ATP and causes smooth muscle contraction.
• D. Nitric oxide is synthesized from epinephrine and causes smooth muscle contraction.

Answer: (B)