Plasma volumes, noradrenaline levels and renin activity during posture changes in end-stage renal failure

Renal nerves in physiology, pathophysiology and interoception

Sympathetic efferent renal nerves have key roles in the regulation of kidney function and blood pressure. Increased renal sympathetic nerve activity is thought to contribute to hypertension by promoting renal sodium retention, renin release and renal vasoconstriction. This hypothesis led to the development of catheter-based renal denervation (RDN) for the treatment of hypertension. Two RDN devices that ablate both efferent and afferent renal nerves received FDA approval for this indication in 2023. However, in animal models, selective ablation of afferent renal nerves resulted in comparable anti-hypertensive effects to ablation of efferent and afferent renal nerves and was associated with a reduction in sympathetic nerve activity. Selective afferent RDN also improved kidney function in a chronic kidney disease model. Notably, the beneficial effects of RDN extend beyond hypertension and chronic kidney disease to other clinical conditions that are associated with elevated sympathetic nerve activity, including heart failure and arrhythmia. These findings suggest that the kidney is an interoceptive organ, as increased renal sensory nerve activity modulates sympathetic activity to other organs. Future studies are needed to translate this knowledge into novel therapies for the treatment of hypertension and other cardiorenal diseases.

Influence of post-exercise activity on plasma catecholamines, blood pressure and heart rate in normal subjects

The purpose of this study was to evaluate whether or not the type of activity performed during recovery might influence the magnitude of catecholamine outflow following exercise. Six active, male volunteers between 40-52 years recovered from strenuous treadmill exercise in three different ways; standing, supine rest and walking (2 mph, 0% grade). Measurements of noradrenaline (NA), adrenaline (A), heart rate and blood pressure were made at rest, peak exercise, and at 30 s intervals through 5-min of recovery. Peak exercise NA concentrations were approximately 1000% above those recorded as rest. Early recovery was marked by a continued increase in NA from peak exercise concentrations (4614 +/- 548 vs. 3264 +/- 485 pg/ml) which did not return to peak exercise levels until approximately 90 s of recovery. Adrenaline responses followed similar trends; however, the changes were not as sizable. Heart rate and diastolic blood pressure were significantly affected by the post-exercise condition; supine recovery produced significantly lower mean heart rates and mean diastolic blood pressures in comparison to standing or continued walking recovery conditions. Thus, these data indicate no specific recovery strategy will stem the rise in exercise-induced plasma catecholamines. Clinically, a strategy of continued walking, or better, supine recovery will best meet special clinical requirements, as well as limit the magnitude of the peak catecholamine increases.

Norepinephrine clearance, chromogranin A and dopamine beta hydroxylase in renal failure

Plasma norepinephrine (NE) levels are normal or elevated in patients with renal failure even though uremia often damages the sympathetic nerves that release NE. We infused 3H-NE into subjects with normal, mildly depressed, or absent renal function. 3H-NE clearance was depressed 20% in mild renal failure and 40% in patients on hemodialysis. The calculated rate of NE release into plasma was low in uremics even though their plasma NE was normal. Dopamine beta hydroxylase (D beta H) and chromogranin A are released from sympathetic nerve endings along with NE. D beta H levels were low in uremia and D beta H levels doubled following hemodialysis. Chromogranin A levels were very high in uremics and increased slightly following hemodialysis. Plasma clearance of both NE and chromogranin A appears low in renal failure. The calculated rate of NE release is diminished in uremics, which is in accord with reports of autonomic neuropathy in these patients.

Effect of changes in posture on circulatory homeostasis in patients with the nephrotic syndrome

To assess whether the upright posture causes circulatory hypovolaemia in patients with the nephrotic syndrome (NS), we studied 12 subjects with NS and 12 healthy subjects during recumbency, 110 min of standing, followed again by recumbency. Control blood-pressure was 134/88 +/- 4/3 mmHg in the patients and 113/75 +/- 2/3 mmHg in the normal subjects (P less than 0.01), and remained higher in the patients throughout the procedure. Heart rate was continuously higher in the patients (P less than 0.05), but acceleration on standing was normal. The blood volume, which was not different during recumbency, had fallen below that in normal subjects after 25 min of standing (P less than 0.05), due to excessive plasma volume reduction (-16.8 +/- 0.8% in the patients against -11.7 +/- 1.2% in the normals, P less than 0.02). Plasma renin activity (PRA) was higher in the patients while recumbent (P less than 0.001) but not during standing, due to a blunted response in some. No significant differences in plasma noradrenaline were found, but four patients reacted with an excessive rise in plasma noradrenaline and heart rate. This subset, which had high PRA levels as well, comprised the only subject who experienced orthostatic hypotension. It is concluded that during standing an excessive drop in plasma volume leads to a lowered blood volume in NS patients. This forms a paradox with the heart rate acceleration and noradrenaline levels, which were mostly normal, and with the blood-pressure, which remained slightly elevated. Even in a few patients with enhanced stimulation of heart rate and noradrenaline, blood-pressure was found to be high in the majority of cases. PRA was usually found to be increased but, in part, independent of posture.