**Core Concept**
The glomerular filtration rate (GFR) is a measure of kidney function that reflects the rate at which the kidneys filter waste products from the blood. The GFR is influenced by several factors, including renal blood flow, glomerular hydrostatic pressure, and the permeability of the glomerular capillaries.

**Why the Correct Answer is Right**
The correct answer is **D. Increased renin release**, which leads to the activation of the renin-angiotensin-aldosterone system (RAAS). This results in increased sodium reabsorption in the collecting ducts, increased blood volume, and consequently increased renal blood flow. As renal blood flow increases, the glomerular hydrostatic pressure also increases, leading to an increase in GFR. This is a classic example of the Frank-Starling mechanism, where an increase in preload (renal blood flow) leads to an increase in stroke volume (GFR).

**Why Each Wrong Option is Incorrect**
**Option A:** Decreased sodium reabsorption in the proximal tubule would lead to a decrease in GFR, not an increase. This is because the proximal tubule is responsible for reabsorbing approximately 70% of the filtered sodium load, and a decrease in reabsorption would lead to a decrease in GFR.

**Option B:** Increased sympathetic tone would actually lead to a decrease in GFR, not an increase. This is because sympathetic tone causes vasoconstriction of the renal arteries, leading to a decrease in renal blood flow and GFR.

**Option C:** Increased antidiuretic hormone (ADH) would lead to increased water reabsorption in the collecting ducts, but this would not directly increase GFR. In fact, increased ADH would lead to increased blood volume, which would increase renal blood flow and GFR indirectly.

**Clinical Pearl / High-Yield Fact**
The RAAS is a crucial regulator of blood pressure and electrolyte balance, and its dysregulation is a key feature of hypertension and heart failure. Understanding the role of the RAAS in regulating GFR is essential for managing patients with kidney disease.

**Correct Answer:** D. Increased renin release leads to activation of the RAAS, increasing renal blood flow and GFR.