Raffaello Golin

Effects of reversible renal denervation on haemodynamic and excretory functions of the ipsilateral and contralateral kidney in the cat.

In anaesthetized cats reversible denervation of one kidney was performed by cooling of the left renal nerves to 3 degrees C for 16 min. The response of the left (ipsilateral) kidney was compared with the response of the right (contralateral) kidney twice in the same animal: (1) when the right kidney was still innervated, and (2) after it had been surgically denervated. Left renal nerve cooling did not cause any changes in arterial pressure. In the left kidney, blood flow, vascular conductance, sodium and water excretions increased, and renin release decreased. Simultaneously in the contralateral kidney, no haemodynamic changes were observed, glomerular filtration was only transiently decreased, whereas sodium and water excretion significantly decreased and renin release increased. When left renal nerve cooling was repeated after surgical denervation of the right kidney, similar changes were observed in the left (ipsilateral) kidney, whereas all contralateral effects were abolished. These experiments suggest that tonically active afferent fibres from one kidney exert a reflex inhibitory action on sympathetic activity directed to the contralateral kidney controlling tubular sodium reabsorption and renin release.

Genetic polymorphism of the renin-angiotensin-aldosterone system and arterial hypertension in the Italian population: The GENIPER Project

Objective To detect the association of single polymorphisms of the renin–angiotensin–aldosterone system (RAAS), or different combinations thereof, with hypertension. Design and methods The GENIPER database is the result of a collaborative effort of 13 Italian research centres to collect genomic DNA in subjects well characterized in terms of blood pressure status. A total of 2461 subjects (normotensive = 611; hypertensive = 1850) were selected and genotyped for the angiotensin-converting enzyme insertion/deletion (ACE I/D), angiotensinogen (AGT) T/C704, angiotensin receptor type 1 (AT1) A/C1166 and aldosterone synthase (ALDO) T/C−344 genetic variants. Results Allele frequencies were homogeneous over the Italian territory, with the relevant exception of the ACE I/D, the D allele being significantly less frequent in the northern region (61%) than in the rest of the country (67%; P < 0.0001). When comparing allele and genotype distributions in normotensives and hypertensives, the latter presented a small but statistically significant increase of the C allele of AGT T/C704, the A allele of AT1 A/C1166 and the T allele of ALDO T/C−344 polymorphisms (P = 0.018, P = 0.037 and P = 0.015, respectively), with similar trends all over the country. A step-wise logistic regression analysis confirmed these findings, by entering in the model as independent predictors of blood pressure status of AGT T/C704 (P = 0.013), ALDO T/C−344 (P = 0.032) and AT1 A/C1166 polymorphisms (P = 0.075), but not ACE I/D (P = 0.996). We also found some evidence of an additive effect of individual genetic variants of the RAAS, modulating at different levels the same functional pathway, on the risk of developing hypertension, but no synergistic interaction was observed. Conclusions Our results suggest that some allelic variants of RAAS genes carry a small but identifiable risk of developing arterial hypertension.

Renal afferents signaling diuretic activity in the cat.

Mechanoreceptors and chemoreceptors have been identified inside the kidney, but their functional role is still largely unclear. The aim of this study was to investigate whether changes in urine output could modify the discharge rate of renal afferent fibers. Experiments were performed in anesthetized cats in which afferent renal nerve activity (ARNA) was recorded by standard electrophysiological techniques from a centrally cut renal nerve. Arterial pressure, renal blood flow velocity, urine flow rate, and renal pelvic pressure were also measured. Three diuretic maneuvers were tested in the same cat: intravenous administration of physiological saline (8 to 13 mL/min for 2 minutes), furosemide (1 mg/kg), and atrial natriuretic peptide (ANP, 1 microgram/kg). The three maneuvers increased urine flow rate and pelvic pressure, respectively, 137.0 +/- 20.6% and 136.8 +/- 21.1% (saline), 148.6 +/- 31.7% and 139.6 +/- 43.5% (furosemide), and 75.9 +/- 7.9% and 62.1 +/- 21.2% (ANP) at the time of the maximum response. Arterial pressure slightly increased after saline, did not change after furosemide, and slightly decreased after ANP. Renal blood flow increased after saline and did not change after furosemide and ANP. The three maneuvers increased ARNA by 98.4 +/- 15.2% (saline), 270.7 +/- 100.8% (furosemide), and 59.6 +/- 23.4% (ANP). Changes in ARNA significantly correlate with changes in both pelvic pressure and urine flow rate. Our data demonstrate that increments in urine flow rate increase the firing rate of renal afferent fibers and suggest that (1) pelvic pressure is the major determinant of the neural response, and (2) this increased afferent discharge is due to activation of renal mechanoreceptors.

Afferent pathways of neural reno-renal reflexes controlling sodium and water excretion in the cat

We have studied the role of afferent renal nerve fibres in anaesthetized cats in mediating the decrease in sodium and water excretion from the contralateral kidney caused by unilateral renal denervation. Transient denervation of one kidney obtained by cooling of the left renal nerves increases contralateral efferent renal nerve activity and decreased sodium and water excretion from the opposite kidney. The results observed in animals with intact neural pathways were compared with those obtained after the left kidney had been selectively deafferentated by cutting the dorsal roots from T9 to L4. Bilateral section of dorsal roots did not affect the increase in sodium and water excretion from the transiently denervated left kidney, but entirely abolished the decrease in sodium and water excretion from the contralateral kidney. Neither the left nor the right dorsal root section alone, affected the response of the contralateral right kidney. Our data demonstrate that afferent renal nerve fibres project bilaterally to the spinal cord and form the afferent branch of the reno-renal reflex by which one kidney can control the function of the opposite one.

Adrenergic sodium handling and the natriuretic action of calcium antagonists.

Stimulation and denervation experiments have provided evidence that adrenergic mechanisms can enhance sodium and water reabsorption from the renal tubule, and that this influence is probably exerted on the entire tubular extent. Reflexes originating from cardio-pulmonary and renal receptors can control adrenergic renal sodium handling, and evidence has recently been presented that a reno-renal reflex tonically inhibits the contralateral sympathetic control of tubular reabsorption of sodium and water. Other investigations indicate that adrenergic renal sodium handling is mediated through α-rather than β-receptors. and that the α-receptors are of the α2-subtype. The question of whether the natriuretic action of calcium antagonists is, at least in part, mediated by interference with adrenergic control of tubular reabsorption cannot yet be definitely answered. Although available data are only preliminary, they do not support an important action of calcium antagonists on adrenergic renal sodium handling, but a separate contribution of impaired adrenergic control and of a direct tubular effect of calcium antagonists cannot be excluded.

Role of the renal nerves in the control of renin synthesis during different sodium intakes in the rat.

Objective The aim of this study was to evaluate the role of the renal nerves in the regulation of renin synthesis in normotensive rats at different sodium balance. Methods Forty-eight male Sprague–Dawley rats were divided in six experimental groups, combining three diets at different NaCl content (normal 0.4%, low 0.04% or high 4.0%), and the surgical, bilateral renal denervation or the sham procedure. After 7 days of dietary treatment, all rats were sacrificed and plasma renin activity (PRA) was measured. Renin messenger RNA (mRNA) levels in the renal cortex were determined by semiquantitative polymerase chain reaction. Results PRA was higher in animals fed the low sodium diet compared with those at standard diet, while it was lower in animals fed the high sodium diet. Renal denervation decreased PRA in normal and low sodium groups, while it did not alter the PRA values in the high sodium group. Renin gene expression significantly increased in rats fed with the low sodium diet compared with the standard diet group, and significantly decreased in rats fed the high sodium diet. Renal denervation significantly reduced renin mRNA levels in rats receiving the low sodium diet, but did not produce any significant change in normal or high-sodium groups. Conclusion The activation of renin gene expression during sodium depletion in rats is dependent on the presence of the renal nerves, while the suppression of renin gene expression during a sodium load seems to be due to the macula densa mechanism alone.

Cardiovascular effects of afferent renal nerve stimulation

Electrical stimulation of afferent renal nerves elicits an increase in arterial pressure and heart rate. The hypertensive response is presumably due to the widespread activation of the sympathetic nervous system leading to peripheral vasoconstriction. Interestingly, the kidney does not appear involved in this reflex excitatory response to afferent renal nerve stimulation since changes in vascular conductances and excretory functions are equal in both the innervated and denervated kidney, and secondary to changes in renal perfusion pressure. In addition, no changes in renin release from either kidneys are observed during afferent renal nerve stimulation. It is likely that the electrical stimulation of afferent renal nerves activates other reflexes exerting an inhibitory influence on efferent renal nerve activity. Indeed, neural renorenal reflexes which tonically inhibit renal functions have clearly been demonstrated. Furthermore, preferential inhibition of efferent renal nerve activity by cardiopulmonary and sinoaortic receptors has recently been shown during activation of other visceral afferents.

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.

Interactions between the sympathetic nervous system and atrial natriuretic factor in the control of renal functions.

We studied neural influences on the renal actions of atrial peptides in anaesthetized cats by comparing the response to atrial natriuretic factor (ANF) infusion in the innervated kidney and in the contralateral surgically denervated kidney. During ANF infusion arterial pressure decreased, the heart rate did not change and blood flow to both kidneys increased slightly. Vascular conductances became slightly but significantly higher in the denervated kidneys than in the controls. In both kidneys, the glomerular filtration rate increased transiently and significantly. Inhibition of renin release was more prompt and larger in the innervated than in the denervated kidneys. ANF infusion caused a significant increase in sodium and water excretion from both the innervated and denervated kidneys. However, the diuretic and natriuretic effect in the innervated kidneys, although proportionally greater than that in the denervated kidneys, was of shorter duration and subsided after 20 min of ANF infusion. Efferent renal nerve activity did not change during the initial 10 min of ANF infusion but thereafter increased progressively and significantly. We conclude that the effects of atrial peptides on renin release and excretory functions are influenced by renal nerve activity.

Neuronal nitric oxide synthase and renin stimulation by sodium deprivation are dependent on the renal nerves

Objective The aim of the present study was to evaluate the role of the renal nerves in the regulation of neuronal nitric oxide synthase (nNOS) gene expression in normotensive rats on different sodium balance. Methods Thirty-six male Sprague–Dawley rats were divided into six experimental groups combining three diets with different NaCl content (normal, 0.4%; low, 0.04%; or high, 4.0%), and bilateral renal denervation or sham denervation. After 7 days of dietary treatment, all rats were sacrificed and plasma renin activity (PRA) measured. The nNOS and renin messenger RNA (mRNA) levels in the renal cortex were determined by semiquantitative polymerase chain reaction. Results PRA was higher in animals with low sodium diet compared with those with standard diet, while it was lower in animals with high sodium diet. Renal denervation decreased PRA in normal and low sodium groups, while it did not alter the PRA values in the high sodium group. The nNOS gene expression significantly increased in rats fed with the low sodium diet compared with the standard diet group, and it significantly decreased in rats with the high sodium diet. Renal denervation significantly reduced nNOS mRNA levels in rats receiving the low sodium diet, but did not significantly influence nNOS mRNA in normal and high sodium groups. Renin mRNA was influenced by diets and denervation in a parallel way to nNOS mRNA. Conclusion The renal nerves mediate the increase of renin and nNOS mRNA during sodium restriction, while the suppression of nNOS and renin gene expression during a sodium load is independent of the presence of the renal nerves. The parallel changes in renin and nNOS mRNA during different sodium intakes suggest that nNOS can be part of the complex, and still largely unclarified, macula densa mechanism of renin regulation.