Differential neural control of intrarenal blood flow

To test whether renal sympathetic nerve activity (RSNA) can differentially regulate blood flow in the renal medulla (MBF) and cortex (CBF) of pentobar bital sodium-anesthetized rabbits, we electrically stimulated the renal ner ves while recording total renal blood flow (RBF), CBF, and MBF. Three stimu lation sequences were applied 1) varying amplitude (0.5-8 V), 2) varying fr equency (0.5-8 Hz), and 3) a modulated sinusoidal pattern of varying freque ncy (0.04-0.72 Hz). Increasing amplitude or frequency of stimulation progre ssively decreased all flow variables. RBF and CBF responded similarly, but MBF responded less. For example, 0.5-V stimulation decreased CBF by 20 +/- 9%, but MBF fell by only 4 +/- 6%. The amplitude of oscillations in all flo w variables was progressively reduced as the frequency of sinusoidal stimul ation was increased. An increased amplitude of oscillation was observed at 0.12 and 0.32 Hz in MBF and to a lesser extent RBF, but not CBF. MBF theref ore appears to be less sensitive than CBF to the magnitude of RSNA, but it is more able to respond to these higher frequencies of neural stimulation.