**Core Concept**
Prostaglandins E1 and E2 are part of the eicosanoid family, which plays a crucial role in mediating inflammation. These prostaglandins act on various receptors to produce their effects.

**Why the Correct Answer is Right**
Prostaglandins E1 and E2 cause vasodilation by stimulating the release of nitric oxide (NO) from endothelial cells. Nitric oxide then activates guanylyl cyclase in smooth muscle cells, leading to the relaxation of vascular smooth muscle and subsequent vasodilation. This is an important mechanism in the inflammatory response, allowing for increased blood flow to the affected area. The vasodilation caused by prostaglandin E1 and E2 also contributes to the increased permeability of blood vessels, leading to the characteristic edema seen in inflammation.

**Why Each Wrong Option is Incorrect**
**Option B:** Increased gastric output is actually caused by prostaglandin E2 through its action on the stomach, but this is not a direct effect of prostaglandin E1.

**Option C:** Decreased body temperature is not a direct effect of prostaglandin E1 or E2. In fact, prostaglandins can cause fever by acting on the hypothalamus to increase the set point for body temperature.

**Option D:** Vasoconstriction is the opposite of the effect caused by prostaglandin E1 and E2. These prostaglandins cause vasodilation, not vasoconstriction.

**Clinical Pearl / High-Yield Fact**
Prostaglandin E2 is also involved in the regulation of gastric acid secretion and is used as a component of certain anti-inflammatory medications, such as misoprostol.

**✓ Correct Answer: A. Vasodilation**