Question

A person is given a drug that dilates the afferent arteriole and constricts the efferent arteriole by the same amounts. Assuming no other actions of the drug, what happens to this person's GFR?

Answer 1

The GFR of this person will increase.

Step-by-step explanation:

The glomerular filtration rate (GFR) will increase since the resistance in the afferent arteriole has decreased because of the arteriole dilatation. In other words, more blood will be filtrated through the glomerulus due to its bigger radius that allows an increase in the blood's flow.

Answer 2

The Glomerular filtration rate (GFR) should increase because of a large increase in the Glomerular capillary hydrostatic pressure (PGC). However, the effect of PGC will be cancelled because of simultaneous dilation of afferent arterioles and constriction of efferent arterioles.

Step-by-step explanation:

The dilation of the afferent arteriole will decrease the filtration fraction which inturn will increase the diameter of glomerular capillaries. Therefore, the Glomerular capillary hydrostatic pressure (PGC) will increase. However, the constriction of efferent arterioles at the same time decreases the GFR and increases the PGC. Therefore, the person's GFR will remain constant and the filtration fraction will remain unchanged thus the effect of increased PGC will be cancelled.