**Core Concept**
Cyclic GMP (cGMP) is a crucial secondary messenger molecule involved in cellular signaling pathways. It plays a vital role in mediating the effects of certain hormones and neurotransmitters by activating downstream targets. cGMP is produced through the activation of guanylyl cyclase, an enzyme that catalyzes the conversion of GTP to cGMP.

**Why the Correct Answer is Right**
Nitric oxide (NO) and atrial natriuretic peptide (ANP) are two key hormones that utilize cGMP as their second messenger. When NO binds to soluble guanylyl cyclase, it activates the enzyme, leading to the production of cGMP. cGMP then activates protein kinase G (PKG), which phosphorylates and activates downstream targets, ultimately resulting in vasodilation and other physiological effects. Similarly, ANP binds to its receptor, which activates guanylyl cyclase and leads to the production of cGMP, contributing to vasodilation and natriuresis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cGMP is not a second messenger for insulin, which primarily utilizes cAMP as its secondary messenger.
**Option B:** This option is incorrect because prostaglandins primarily utilize cAMP as their second messenger, not cGMP.
**Option C:** This option is incorrect because dopamine does not directly use cGMP as its second messenger; it primarily utilizes cAMP.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the nitric oxide-cGMP pathway plays a crucial role in vasodilation and is often targeted in the treatment of conditions like pulmonary hypertension.

**Correct Answer: C. Nitric oxide (NO) and atrial natriuretic peptide (ANP)**