Increased sympathetic nervous system activity primarily affects the glomerular filtration rate (GFR) by causing vasoconstriction of which renal arteriole?

✓ Correct Answer: Option A

Increased sympathetic activity causes vasoconstriction of the afferent arteriole, reducing blood flow into the glomerulus. This decreases glomerular capillary hydrostatic pressure, thereby decreasing the glomerular filtration rate (GFR).