Renal function and renal afferent and efferent nerve activity.

Recent microperfusion studies have fully substantiated the direct action of catecholamines on renal tubular reabsorptive rates. Surprisingly, these techniques have not provided consistent information on the nature of the adrenoceptor responsible for the stimulation of proximal tubular reabsorption. Both alpha- and beta-receptors have been favored for this role. These techniques have confirmed earlier reports that dopamine may have a direct natriuretic action on the renal tubules. The demonstration that renal efferent nerves contain both noradrenergic and dopaminergic fibers lends further support for the participation of dopamine in the regulation of salt and water excretion. Efferent renal nerve activity is modulated by a number of different afferent inputs to the central nervous system. One of these is the renal afferent innervation, which is composed of both chemoreceptor and mechanoreceptor fibers. A number of different reflexes that affect efferent renal nerve activity have been identified by electrical stimulation of renal afferent nerves or by selective stimulation of renal mechanoreceptors and chemoreceptors. These renorenal reflexes may have importance in the coordination of excretory activity between the two kidneys. Studies of these aspects of renal nerve function are reviewed. The importance of the renal nerves in conscious animals is also discussed in the light of evidence that their influence on renal function may be more apparent in abnormal or pathological circumstances.