**Core Concept**
The loop of Henle is a critical component of the nephron, responsible for the countercurrent multiplier system, which helps to concentrate or dilute the urine based on the body's needs. The flow through the loop of Henle affects the reabsorption and secretion of ions and water.

**Why the Correct Answer is Right**
Increased flow through the loop of Henle leads to a decrease in the glomerular filtration rate (GFR) due to the increased pressure in the peritubular capillaries. This increased pressure decreases the hydrostatic pressure in the glomerulus, leading to a decrease in GFR. The increased flow also leads to increased reabsorption of ions and water in the thick ascending limb of the loop of Henle, which further contributes to the decrease in GFR.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the decrease in GFR due to increased flow through the loop of Henle.
* **Option B:** Vasopressin increases water reabsorption in the collecting duct, but it does not directly affect GFR.
* **Option C:** Angiotensin II increases blood pressure, but it does not directly decrease GFR due to increased flow through the loop of Henle.

**Clinical Pearl / High-Yield Fact**
The loop of Henle is sensitive to changes in flow and pressure, and alterations in its function can lead to changes in GFR and urine concentration.

**Correct Answer: C. Angiotensin II increases blood pressure, but it does not directly decrease GFR due to increased flow through the loop of Henle.**