Der Einflu� der Kreislauff�llung auf die Aktivit�t der Nierennerven beim Frosch

Effect of splanchnicotomy on the renal excretion of uric acid in anaesthetized dogs

The renal excretion of uric acid was examined during acute i.v. urate (Ua) loading on unilaterally splanchnicotomized ("renal denervation") anaesthetized mongrel dogs. Glomerular filtration rate (GFR) in general was not different in innervated and denervated kidneys, whereas urine flow (V) and urinary excretion of sodium (UNaV) on the splanchnicotomized side were significantly increased at any plasma concentration of Ua. The excretion (UUaV) and tubular transport (TUa) of urate calculated for unit GFR were considerably increased and depressed, respectively, at normal plasma Ua level and during minor urate loading (plasma concentration up to 4.7 mg%). Above this plasma level, i.e. up to 24.6 mg%, no difference in net urate reabsorption between intact and sympathectomized organs was found. It is suggested that both reabsorption and secretion of Ua in denervated kidneys are diminished.

Reduction of renal nerve activity by volume expansion in conscious cats

In conscious cats with intact or denervated baroreceptors volume expansion of 5-15% of blood volume was performed with dextran and isotonic sodium chloride. Renal sympathetic activity (RSA), electroencephalogram (EEG) blood pressure (BP) and heart rate (HR) were recorded. RSA was reduced by 25-85% in 10 experiments out of 11 by volume expansion both with dextran and isotonic sodium chloride. Reduction of RSA could not be related to different states of wakefulness as indicated by the EEG, so could only be caused by volume expansion, although no quantitative correlation could be detected. No differences were observed between animals with intact and denervated baroreceptor. In most experiments BP and HR decreased during volume expansion up to -25 mmHg and up to -23 beats/min, respectively. The degree of BP and HR reduction could not be related to the degree of RSA reduction. The results suggest that changes in RSA might be involved in the renal response to volume expansion.

Contribution of Baroreceptors to the Control of Renal Function

Electrical stimulation of the left stellate ganglion of the dog is associated with an increase in urine flow, in electrolyte and total solute excretion, and in the renal clearance of inulin. These changes appear rapidly, are well maintained during prolonged stimulation, and stop soon after stimulation has ceased. The hemodynamic responses associated with these changes are an increase in arterial pulse pressure, an increase or no change in mean arterial blood pressure, and a decline in mean left atrial pressure. The diuretic response to stellate ganglion stimulation is diminished, but not abolished, by bilateral cervical vagotomy as are the changes in electrolyte excretion, total solute excretion, and the renal clearance of inulin. However, the hemodynamic responses are not greatly modified by cervical vagotomy. Vagotomy just above the diaphragm does not appear to modify these responses. The effect of vagotomy on the renal responses to stellate stimulation appears to be a result of sectioning baroreceptor afferent nerves which traverse the vagus nerves. The rapidity of the renal response to stellate stimulation, its temporal relation to the hemodynamic changes, and the effect of cervical vagotomy indicate that the diuresis is, to a large degree, secondary to withdrawal of renal sympathetic vasoconstrictor nerve discharge. The similarities between the renal responses to stellate stimulation and to intravenous infusions indicate that infusion diuresis may be mediated, at least in part, by the same mechanism.

When renal blood flow is measured directly in the perfused kidney, carotid occlusion is associated with little change or with a decrease in renal blood flow at a time when renal arterial pressure increases. When renal blood flow is maintained constant in the perfused kidney, carotid artery occlusion is associated with an increase in renal arterial pressure. The intrarenal administration of the adrenergic blocking agent, phenoxybenzamine, can prevent the increase in renal vascular resistance during carotid occlusion indicating that it is due to an adrenergic mechanism. The renal pressure-flow curve is displaced down and to the right during carotid occlusion; autoregulation of renal blood flow is still observed, although at a lower level of blood flow. All these changes indicate that the primary renal response to carotid occlusion is vasoconstriction mediated by the renal sympathetic nerves.

It is well-known that urine flow increases when renal arterial pressure is increased independent of a change in the activity of the renal vasoconstrictor nerves and independent of a change in renal blood flow. Consequently, the rise in arterial pressure associated with carotid occlusion can contribute directly to the response of the kidney to carotid occlusion. The variability of the changes in water and electrolyte excretion by the kidney during carotid occlusion may represent a varying contribution of direct and reflex mechanisms to the total response.