**Core Concept**
Oxytocin is a hormone involved in social bonding, labor, and lactation. It exerts its effects by binding to specific receptors on the surface of target cells, which triggers a signaling cascade that ultimately influences various physiological processes. The second messenger system is a crucial component of this signaling pathway.

**Why the Correct Answer is Right**
Oxytocin binds to its receptor, a G protein-coupled receptor, which activates a Gq protein. This leads to the activation of phospholipase C (PLC), which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 then acts as a second messenger to increase intracellular calcium levels, which triggers muscle contraction in the uterus during labor.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because oxytocin's primary action is not mediated by cyclic AMP (cAMP) as a second messenger.
**Option B:** Incorrect because the second messenger for oxytocin is not cyclic GMP (cGMP).
**Option C:** Incorrect because the second messenger for oxytocin is not arachidonic acid.

**Clinical Pearl / High-Yield Fact**
Oxytocin's effects on uterine smooth muscle are mediated by an increase in intracellular calcium levels triggered by IP3, which is a key factor in the initiation of labor.

**Correct Answer: C. IP3**