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1 Circulatory Control Laboratory, Departments of Physiology and Electrical and Electronic Engineering, and 3 Biostatistics Unit, Division of Community Health, University of Auckland, Auckland, New Zealand; and 2 Department of Physiology, Monash University, Melbourne, 3800 Australia
We tested for regional differences in perfusion responses, within the renal medulla and cortex, to renal nerve stimulation in pentobarbital sodium-anesthetized rabbits. Laser-Doppler flux (LDF) was monitored at various depths below the cortical surface (1-15 mm). Basal cortical LDF (1-3 mm, ~200-450 U) was greater than medullary LDF (5-15 mm, ~70-160 U), but there were no statistically significant differences in basal LDF within these regions. The background LDF signal during aortic occlusion was similar in the cortex (2 mm, 31 U) and outer medulla (7 mm, 31 U), but slightly greater in the inner medulla (12 mm, 44 U). During electrical stimulation of the renal nerves (0.5-8 Hz), cortical LDF and total renal blood flow were similarly progressively reduced with increasing stimulus frequency. Medullary LDF (measured between 5 and 15 mm) was overall less responsive than cortical LDF. For example, 4-Hz stimulation reduced inner medullary LDF (9 mm) by 19 ± 6% but reduced cortical LDF (1 mm) by 54 ± 11%. However, medullary LDF responses to nerve stimulation were similar at all depths measured. Our results indicate that while the vascular elements controlling medullary perfusion are less sensitive to the effects of electrical stimulation of the renal nerves than are those controlling cortical perfusion, sensitivity within these vascular territories appears to be relatively homogeneous.
laser-Doppler flowmetry; medullary blood flow; rabbit; renal blood flow; sympathetic nervous system
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