What is the effect of Viagra on cyclic GMP levels and smooth muscle contraction in erectile function?

• A. Viagra activates phosphodiesterase, decreasing cyclic GMP levels, which reduces smooth muscle contraction and blood flow in the penis.
• B. Viagra increases nitric oxide synthesis, which decreases cyclic GMP levels and smooth muscle contraction.
• C. Viagra inhibits phosphodiesterase, increasing cyclic GMP levels, which enhances smooth muscle contraction and maintains blood flow in the penis.
• D. Viagra inhibits cyclic AMP production, leading to increased smooth muscle contraction and blood flow in the penis.

Answer: (C)