Graded increases in renal nerve activity with hypoxia in conscious rabbits: renal hemodynamic and excretory responses. Malpas, Simon C., Amany Shweta, Warwick P. Anderson & Geoffrey A. Head. Baker Medical Research Institute, Prahran, Victoria, Australia
APStracts 3:0214R, 1996.
Changes in renal sympathetic nerve activity are postulated to influence renal function in selective ways; such that different levels of activation produce particular renal responses, initially in renin release, then sodium excretion, with changes in renal hemodynamics occurring only with much greater stimulus intensities. The aim of this study was to determine the renal hemodynamic, and excretory responses to graded physiological increases in renal sympathetic nerve activity, induced by breathing different hypoxic gas mixtures. Experiments were performed in seven conscious rabbits subjected to 4 gas mixtures (14% O2, 10%O2, 10%O2+3%CO2 and 10%O2+5%CO2) and instrumented for recording of renal nerve activity. Following a 30 min control period, rabbits were subjected to one of the four gas mixtures for 30 min and then room air was resumed for a further 30 min. The four gas mixtures increased renal sympathetic activity (SNA) by 14, 38, 49 and 165% respectively, but arterial pressure (thus renal perfusion pressure) was not altered by any of the gas mixtures. The greatest level of sympathetic activation produced significant falls in glomerular filtration rate (GFR), renal blood flow, sodium and fluid excretion and significant increases in plasma renin activity. These returned to levels not significantly different from control conditions in the 30 min period after the gas mixture. When the changes to the various gas mixtures were analyzed within each rabbit, a significant linear relationship was found with all variables to the increase in SNA. Renal denervation in a separate group of 7 rabbits completely abolished all of the above responses to the different gas mixtures. Thus, graded activation of renal nerves induced by changes in inspired gas mixtures resulted in graded decreases in renal blood flow, GFR and sodium excretion and graded increases in renin activity, with the changes occurring across a similar range of nerve activities and there was no evidence for a selective change in any renal variable. 

Received 28 December 1995; accepted in final form 21 May 1996.
APS Manuscript Number R822-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96