<prompt> Answer this question truthfullyHow can effective renal plasma flow be estimated using an equation and what are the variables involved?  <response>: <reason> Effective renal plasma flow may be estimated using the equation: eRPF PAH UPAH V PPAH, where PAH represents para-aminohippuric acid, UPAH is the concentration of PAH in urine, PPAH is the concentration of PAH in plasma, and V is the urine flow rate. 