Resonance in the renal vasculature evoked by activation of the sympathetic nerves.
We examined the ability of different frequencies in sympathetic nerve activity (SNA) to induce oscillations in renal blood flow (RBF). In anesthetized rabbits the renal nerves were stimulated using modulated sine patterns (base frequency 5 Hz, 5-ms duration pulses) that varied in amplitude between 0 and 10 V at a frequency between 0.04 and 1.0 Hz. The strengths of the induced oscillations in RBF were calculated using spectral analysis. Although faster rhythms in simulated SNA >0.6 Hz contributed to the level of vascular tone, 95% of the power in the frequency response curve was below this frequency, indicating a low-pass filtering/integrating characteristic of the vasculature. Frequencies <0.6 Hz were associated with increasing ability to induce oscillations in RBF. The ability of an SNA rhythm at 0.6 Hz to induce a rhythm in RBF was 21 times less than that at 0.25 Hz. At 0.16 Hz there was a distinct peak in the frequency response curve, indicating the vasculature was more sensitive in this frequency band to sympathetic stimulation. Blockade of endogenous nitric oxide by NG-nitro-L-arginine methyl ester (L-NAME; 20 mg/kg) did not alter resting RBF levels nor was the low-pass filtering/integrating characteristic of the vasculature to nerve stimulation changed (i.e., the curve was not shifted left or right); however, there was a selective increase in the sensitivity to stimulation at 0.16 Hz, i.e., larger oscillations in RBF were evoked. These results indicate an ability of SNA to induce resonant oscillations in the renal vasculature and that there may be active and passive modulators of these responses. Naturally occurring oscillations in SNA <0.6 Hz are likely to contribute to the dynamic control of RBF, ensuring it responds rapidly and with high gain to the stimuli of daily life, while filtering out the faster oscillations ensures stable glomerular filtration.
Malpas
S C
SC
Department of Physiology, University of Auckland, New Zealand.
Hore
T A
TA
Navakatikyan
M
M
Lukoshkova
E V
EV
Nguang
S K
SK
Austin
P C
PC
D000818:Animals; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005919:Glomerular Filtration Rate; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D010507:Periodicity; D011817:Rabbits; D012077:Renal Artery / Q000294:innervation*; D012079:Renal Circulation / Q000187:drug effects / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D014462:Ultrafiltration
D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D019331:NG-Nitroarginine Methyl Ester