Final answer:
The sympathetic nervous system decreases glomerular filtration rate by inducing the constriction of the afferent arterioles, decreasing blood flow to the glomeruli, and indirectly affecting both arterioles through the actions of angiotensin II.
Step-by-step explanation:
The sympathetic nervous system decreases glomerular filtration rate (GFR) primarily through the stimulation of the constriction of the afferent arterioles. This is achieved by the release of norepinephrine, which leads to vasoconstriction and reduces the volume of blood flowing into the glomeruli. Additionally, the sympathetic nervous system can increase the production of angiotensin II, which further constricts both afferent and efferent arterioles, reducing GFR and renal blood flow to preserve blood volume especially during instances of blood loss or dehydration. While the direct sympathetic response acts predominantly on the afferent arterioles, the downstream effects of sympathetic stimulation on renin release and angiotensin II production affect both arterioles.