Final answer:
An increase in afferent arteriolar resistance reduces the glomerular filtration rate by constricting blood flow to the glomeruli, caused by responses like the myogenic mechanism and tubuloglomerular feedback. The correct answer is B) An increase in afferent arteriolar resistance.
Step-by-step explanation:
The question relates to the mechanisms regulating the glomerular filtration rate (GFR) in the kidneys. An increase in afferent arteriolar resistance will reduce GFR. When the afferent arterioles constrict, less blood reaches the glomeruli, decreasing the pressure inside the glomerular capillaries and thereby reducing GFR. This can occur via the myogenic mechanism when arteriole smooth muscle cells contract in response to increased blood pressure or through tubuloglomerular feedback when high filtrate osmolarity and flow rate cause macula densa cells to stimulate arteriole constriction.
Therefore, the correct answer is B) An increase in afferent arteriolar resistance. Options A, C, D, and E generally contribute to an increase in GFR by either decreasing resistance or increasing pressure and blood flow through the kidneys.