pr20 wrote:
Answer is B.

Renal blood flow = (renal artery pressure - renal vein pressure)/renal vascular resistance(RVR).Therefore,if RVR is decreased to half its original value,with no pressure changes,renal blood flow must double (not increase 50%).Increased blood flow to the kidney and pressure in the glomerular capillaries increase renal oxygen use by increasing GFR,which increases the filtered load of sodium and other solutes.Since active sodium reabsorbtion is load dependent,increased tubular fluid sodium increases all active sodium reasorbtion,which requires more ATP hydrolysis and synthesis( and hence more oxygen use).Renal artery concentration does not change,since it is dependent on normal lung function,not oxygen extraction by the kidney.