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

Viagra activates phosphodiesterase, decreasing cyclic GMP levels, which reduces smooth muscle contraction and blood flow in the penis.

Viagra increases nitric oxide synthesis, which decreases cyclic GMP levels and smooth muscle contraction.

Viagra inhibits phosphodiesterase, increasing cyclic GMP levels, which enhances smooth muscle contraction and maintains blood flow in the penis.

Viagra inhibits cyclic AMP production, leading to increased smooth muscle contraction and blood flow in the penis.