Neural control of the kidney--are there reno-renal reflexes?

Circulatory, secretory (renin release) and excretory (tubular sodium and water reabsorption) renal functions are known to be under neural control exerted by sympathetic fibers. Influences on circulatory and secretory functions are modulated by vagally mediated reflexes originated from low pressure (or volume) receptors in the cardiopulmonary area. The possibility that reno-renal reflexes may also exist has raised interest recently. Mechanoreceptors and chemoreceptors have been described in the kidney, and electrophysiological evidence of reno-renal reflexes is available. However, electrical stimulation of afferent renal nerves has failed to reflexly influence circulatory, secretory and excretory functions of the contralateral kidney. Deafferentation studies have been more successful, however. Transient denervation of one kidney by renal nerve cooling is accompanied by reduction of sodium and water excretion from the contralateral kidney with negligible changes in blood flow and glomerular filtration rate. The contralateral antidiuretic activity is prevented either by denervation of the contralateral kidney or by interruption of the afferent fibers running in the spinal dorsal roots. This definitely shows that a reno-renal reflex exists, consisting in a tonic inhibition of contralateral sympathetic activity controlling tubular reabsorption of sodium and water, and renin release.