From the Research
Yes, renal plasma flow does affect glomerular filtration in addition to glomerular capillary pressure, as evidenced by the correlation between changes in renal plasma flow and glomerular filtration rate found in a study published in 2009 1. The mathematical expression for this relationship is given by the filtration fraction (FF) equation: FF = GFR/RPF, where GFR is glomerular filtration rate and RPF is renal plasma flow. Alternatively, the more comprehensive equation for GFR is the Starling forces equation: GFR = Kf × [(PGC - PBS) - (πGC - πBS)], where Kf is the filtration coefficient, PGC is glomerular capillary hydrostatic pressure, PBS is Bowman's space hydrostatic pressure, πGC is glomerular capillary oncotic pressure, and πBS is Bowman's space oncotic pressure. Renal plasma flow affects GFR by influencing the oncotic pressure gradient along the glomerular capillaries, as supported by a study from 1980 which suggests that changes in the rate of nephron plasma flow are a major determining factor in glomerular ultrafiltration 2. As plasma flows through the glomerulus, protein concentration increases as water is filtered out, raising the oncotic pressure and progressively reducing the filtration force. Higher plasma flow rates minimize this protein concentration effect, maintaining a higher filtration rate. This is why conditions that reduce renal plasma flow, such as dehydration or heart failure, typically cause a corresponding decrease in GFR, while increased renal plasma flow from medications like dopamine can increase GFR. Additionally, age-associated changes in renal function, including decreases in glomerular filtration rate and renal blood flow, further highlight the importance of renal plasma flow in glomerular filtration, as noted in a 2010 study on the aging kidney 3. The relationship between renal plasma flow and glomerular filtration rate is also influenced by other factors, such as glomerular capillary pressure, which can be affected by various physiological and pathological conditions, as discussed in a 1991 study on glomerular capillary pressure and hypertension 4.