**Core Concept**
Ferroportin is a transmembrane protein responsible for exporting iron from cells. Its release and activity are tightly regulated by various mechanisms to maintain iron homeostasis in the body.

**Why the Correct Answer is Right**
The release of ferroportin is primarily controlled by hepcidin, a peptide hormone produced by the liver. Hepcidin binds to ferroportin, causing its internalization and degradation, thereby regulating iron export from cells. This mechanism is crucial for maintaining iron balance and preventing iron overload or deficiency. Hepcidin levels are influenced by factors such as iron stores, erythropoietic activity, and inflammation.

**Why Each Wrong Option is Incorrect**
**Option A:** is incorrect because it does not accurately describe the primary regulator of ferroportin release.
**Option B:** is incorrect as it is not directly involved in the regulation of ferroportin.
**Option C:** is incorrect as it is not a known regulator of ferroportin release.

**Clinical Pearl / High-Yield Fact**
Hepcidin-ferroportin interaction is a key mechanism in maintaining iron homeostasis. Dysregulation of this pathway is associated with disorders such as hereditary hemochromatosis and anemia of chronic disease.

**Correct Answer:** D. Hepcidin