Renal sensory receptor activation by calcitonin gene-related peptide

Fetal Undernutrition Programming, Sympathetic Nerve Activity, and Arterial Hypertension Development

A wealth of evidence showed that low birth weight is associated with environmental disruption during gestation, triggering embryotic or fetal adaptations and increasing the susceptibility of progeny to non-communicable diseases, including metabolic and cardiovascular diseases, obesity, and arterial hypertension. In addition, dietary disturbance during pregnancy in animal models has highlighted mechanisms that involve the genesis of arterial hypertension, particularly severe maternal low-protein intake (LP). Functional studies demonstrated that maternal low-protein intake leads to the renal decrease of sodium excretion and the dysfunction of the renin-angiotensin-aldosterone system signaling of LP offspring. The antinatriuretic effect is accentuated by a reduced number of nephron units and glomerulosclerosis, which are critical in establishing arterial hypertension phenotype. Also, in this way, studies have shown that the overactivity of the central and peripheral sympathetic nervous system occurs due to reduced sensory (afferent) renal nerve activity. As a result of this reciprocal and abnormal renorenal reflex, there is an enhanced tubule sodium proximal sodium reabsorption, which, at least in part, contributes directly to arterial hypertension development in some of the programmed models. A recent study has observed that significant changes in adrenal medulla secretion could be involved in the pathophysiological process of increasing blood pressure. Thus, this review aims to compile studies that link the central and peripheral sympathetic system activity mechanisms on water and salt handle and blood pressure control in the maternal protein-restricted offspring. Besides, these pathophysiological mechanisms mainly may involve the modulation of neurokinins and catecholamines pathways.

Chronic intermittent hypoxia impairs diuretic and natriuretic responses to volume expansion in rats with preserved low-pressure baroreflex control of the kidney

We examined the effects of exposure to chronic intermittent hypoxia (CIH) on baroreflex control of renal sympathetic nerve activity (RSNA) and renal excretory responses to volume expansion (VE) before and after intrarenal transient receptor potential vanilloid 1 (TRPV1) blockade by capsaizepine (CPZ). Male Wistar rats were exposed to 96 cycles of hypoxia per day for 14 days (CIH) or normoxia. Urine flow and absolute Na+ excretion during VE were less in CIH-exposed rats, but the progressive decrease in RSNA during VE was preserved. Assessment of the high-pressure baroreflex revealed an increase in the operating and response range of RSNA and decreased slope in CIH-exposed rats with substantial hypertension [+19 mmHg basal mean arterial pressure (MAP)] but not in a second cohort with modest hypertension (+12 mmHg). Intrarenal CPZ caused diuresis, natriuresis, and a reduction in MAP in sham-exposed (sham) and CIH-exposed rats. After intrarenal CPZ, diuretic and natriuretic responses to VE in CIH-exposed rats were equivalent to those of sham rats. TRPV1 expression in the renal pelvic wall was similar in both experimental groups. Exposure to CIH did not elicit glomerular hypertrophy, renal inflammation, or oxidative stress. We conclude that exposure to CIH 1) does not impair the low-pressure baroreflex control of RSNA; 2) has modest effects on the high-pressure baroreflex control of RSNA, most likely indirectly due to hypertension; 3) can elicit hypertension in the absence of kidney injury; and 4) impairs diuretic and natriuretic responses to fluid overload. Our results suggest that exposure to CIH causes renal dysfunction, which may be relevant to obstructive sleep apnea.

Is Aberrant Reno-Renal Reflex Control of Blood Pressure a Contributor to Chronic Intermittent Hypoxia-Induced Hypertension?

Renal sensory nerves are important in the regulation of body fluid and electrolyte homeostasis, and blood pressure. Activation of renal mechanoreceptor afferents triggers a negative feedback reno-renal reflex that leads to the inhibition of sympathetic nervous outflow. Conversely, activation of renal chemoreceptor afferents elicits reflex sympathoexcitation. Dysregulation of reno-renal reflexes by suppression of the inhibitory reflex and/or activation of the excitatory reflex impairs blood pressure control, predisposing to hypertension. Obstructive sleep apnoea syndrome (OSAS) is causally related to hypertension. Renal denervation in patients with OSAS or in experimental models of chronic intermittent hypoxia (CIH), a cardinal feature of OSAS due to recurrent apnoeas (pauses in breathing), results in a decrease in circulating norepinephrine levels and attenuation of hypertension. The mechanism of the beneficial effect of renal denervation on blood pressure control in models of CIH and OSAS is not fully understood, since renal denervation interrupts renal afferent signaling to the brain and sympathetic efferent signals to the kidneys. Herein, we consider the currently proposed mechanisms involved in the development of hypertension in CIH disease models with a focus on oxidative and inflammatory mediators in the kidneys and their potential influence on renal afferent control of blood pressure, with wider consideration of the evidence available from a variety of hypertension models. We draw focus to the potential contribution of aberrant renal afferent signaling in the development, maintenance and progression of high blood pressure, which may have relevance to CIH-induced hypertension.

Effect of intracerebroventricular epinephrine microinjection on blood pressure and urinary sodium handling in gestational protein-restricted male adult rat offspring

In this study, we hypothesized that blunting of the natriuresis response to intracerebroventricularly (ICV) microinjected adrenergic agonists is involved in the development of hypertension in maternal low-protein intake (LP) offspring. A stainless steel cannula was stereotaxically implanted into the right lateral ventricle (LV), then we evaluated the ICV administration of adrenergic agonists at increasing concentrations, and of α1 and α2-adrenoceptor antagonists on blood pressure and urinary sodium handling in LP offspring relative to an age-matched normal-protein intake (NP) group. We confirmed that epinephrine (Epi) microinjected into the LV of conscious NP rats leads to enhanced natriuresis followed by a reduction in arterial pressure. This response is associated with increased proximal and post-proximal sodium excretion accompanied by an unchanged glomerular filtration rate. The current study showed, in both NP and LP offspring, that the natriuretic effect of Epi injection into the LV was abolished by prior local microinjection of an α1-adrenoceptor antagonist (prazosin). Conversely, LV α2-adrenoceptor antagonist (yohimbine) administration potentiated the action of Epi. The LV yohimbine pretreatment normalized urinary sodium excretion and reduced the blood pressure in LP compared with age-matched NP offspring. These are, as far as we are aware, the first results showing the role of central adrenergic receptors’ interaction on hypertension pathogenesis in maternal LP fetal-programming offspring. This study also provides good evidence for the existence of central nervous system adrenergic mechanisms consisting of α1 and α2-adrenoceptors, which work reciprocally on the control of renal sodium excretion and blood pressure. Although the precise mechanism of the different natriuretic response of NP and LP rats is still uncertain, these results lead us to speculate that inappropriate neural adrenergic pathways might have significant effects on tubule sodium transport, resulting in the inability of the kidneys to control hydrosaline balance and, consequently, an increase in blood pressure.

Summary: We evaluated the effect of intracerebroventricular microinjections of adrenergic agonists at increasing concentrations, and μ1 and μ2-adrenergic receptors antagonists on blood pressure and urinary sodium in hypertensive low- and normal-protein rat offdpring.

Altered urinary sodium excretion response after central cholinergic and adrenergic stimulation of adult spontaneously hypertensive rats

In this study, we hypothesized that blunting of the natriuresis response to intracerebroventricularly (i.c.v.) microinjected cholinergic and adrenergic agonists is involved in the development of hypertension in spontaneously hypertensive rats (SHR). We evaluated the effect of i.c.v. injection of cholinergic and noradrenergic agonists, at increasing concentrations, and of muscarinic cholinergic and α1 and α2-adrenoceptor antagonists on blood pressure and urinary sodium handling in SHR, compared with age-matched Wistar Kyoto rats (WR). We confirmed that CCh and NE microinjected into the lateral ventricle (LV) of conscious rats leads to enhanced natriuresis. This response was associated with increased proximal and post-proximal sodium excretion accompanied by an unchanged rate of glomerular filtration. We showed that cholinergic-induced natriuresis in WR and SHR was attenuated by previous i.c.v. administration of atropine and was significantly lower in the hypertensive strain than in WR. In both groups the natriuretic effect of injection of noradrenaline into the LV was abolished by previous local injection of an α1-adrenoceptor antagonist (prazosin). Conversely, LV α2-adrenoceptor antagonist (yohimbine) administration potentiated the action of noradrenaline. The LV yohimbine pretreatment normalized urinary sodium excretion in SHR compared with age-matched WR. In conclusion, these are, as far as we are aware, the first results showing the importance of interaction of central cholinergic and/or noradrenergic receptors in the pathogenesis of spontaneous hypertension. These experiments also provide good evidence of the existence of a central adrenergic mechanism consisting of α1 and α2-adrenoceptors which works antagonistically on regulation of renal sodium excretion.

Segmental regulation of sodium and water excretion by TRPV1 activation in the kidney

Our previous studies show that activation of the transient receptor potential vanilloid type 1 (TRPV1) channels by a selective agonist, capsaicin (CAP), given unilaterally into the renal pelvis leads to increases in urine flow rate (Uflow) and urinary sodium excretion (UNa) bilaterally, although the mechanisms underlying enhanced renal excretory function are unknown. The present study was designed to determine the contribution of each of the renal segments to enhanced renal excretory function when TRPV1 expressed in sensory nerve fibers innervating the renal pelvis is activated. To accomplish the goal, LiCl was given intravenously to male Wistar rats while the left renal pelvis (LRP) was perfused with vehicle or CAP with or without a selective TRPV1 antagonist, capsazepine (CAPZ). Uflow and clearance of creatinine, lithium, sodium, and water, either filtered or fractionally, were determined in both kidneys. LRP perfusion of CAP at 2.4 nmol increased Uflow (microL.ming; ipsilaterally from 6.6 +/- 0.6 to 14.6 +/- 2.2 and contralaterally from 7.4 +/- 0.7 to 13.9 +/- 1.8, P < 0.05) and UNa (micromol.ming; ipsilaterally from 0.6 +/- 0.2 to 1.8 +/- 0.3 and contralaterally from 0.7 +/- 0.2 to 1.9 +/- 0.4, P < 0.05). Ipsilateral blockade of the TRPV1 with CAPZ at 24 nmol prevented CAP-induced increases in Uflow and UNa bilaterally. Creatinine, lithium, sodium, and free water clearance (ml.min) were increased in CAP (1.47 +/- 0.27, 0.44 +/- 0.05, 0.026 +/- 0.004, 0.41 +/- 0.05, respectively) compared to vehicle (0.72 +/- 0.12, 0.25 +/- 0.05, 0.010 +/- 0.001, 0.24 +/- 0.05), CAPZ+CAP (0.83 +/- 0.13, 0.24 +/- 0.03, 0.014 +/- 0.002, 0.23 +/- 0.03), and CAPZ (0.88 +/- 0.05, 0.21 +/- 0.01, 0.010 +/- 0.001, 0.20 +/- 0.01) groups (P <or= 0.01). Filtered sodium load, distal delivery of sodium, and distal sodium reabsorption (muEq.min) were also increased in CAP (202.2 +/- 33.3, 61.3 +/- 7.4, 57.6 +/- 7.4, respectively) compared to vehicle (97.7 +/- 16.6, 33.6 +/- 5.8, 32.2 +/- 5.9), CAPZ+CAP (110.5 +/- 16.3, 32.5 +/- 4.5, 30.7 +/- 4.3), and CAPZ (118.0 +/- 4.5, 27.9 +/- 1.2, 26.8 +/- 1.2) groups (P <or= 0.01). In contrast, fractional lithium and sodium excretion, absolute proximal reabsorption, fractional proximal reabsorption, fractional distal sodium, and water reabsorption were not different among groups. Therefore, activation of the TRPV1 expressed in primary afferent nerves innervating the renal pelvis leads to diuresis and natriuresis in both kidneys. The TRPV1-induced sodium and water excretion appears to be mediated by increases in glomerular filtration rate and distal tubular delivery of sodium but not by suppression of renal proximal and distal tubular reabsorption, suggesting a key role of segmental regulation of renal function by TRPV1-positive primary sensory nerves in the maintenance of sodium and water homeostasis.

Renal contribution to thermolability in rats: role of renal nerves

BACKGROUND

Body temperature is closely regulated via the integration of a number of mechanisms, the study of which has been greatly assisted by the exploitation of comparative physiology. Previous studies have demonstrated that chronic renal failure patients have significantly lower body temperatures than healthy subjects when artifacts from circadian changes were taken into consideration. We hypothesize that the blunting of renal sensory neurons after kidney partial ablation may contribute to the lack of suppression of sympathetic efferent outflow towards BAT, modifying the glucose metabolism signaling pathway, UCP 1 expression and liver mitocondrial respiratory chain activity.

METHODS

To evaluate the influence of renal mass reduction, renal denervation and chronic deafferentation by capsaicin on thermoregulation, glucose metabolism, UCP1 expression and liver mitocondrial respiration, was used respectively, the blocking of heat dissipation by thermoneutral body water immersion, the oxygen consumption by Clark-type electrode, and western blot method.

RESULTS

The study confirmed that, following 5/6 nephrectomy, the basal core temperature of rats was significantly lower than that of control animals when maintained in a thermoneutral body water immersion recipient, as compared to controls. Additionally, we demonstrated that exposure of bilateral renal denervated or of renal chronic capsaicin-treated rats to a similar experimental protocol results in a fast and high rise in rectal temperature response, and this is associated with a significant increase in the basal serine phosphorylation and protein levels of Akt and protein levels of UCP1. This was observed despite unchanged liver mitochondria respiratory control and ADP/O ratios in 5/6 Nx, as well as DNx, when compared to control mitochondria.

CONCLUSIONS

Speculatively, it may be suggested that one of the renal sensory nerve signal defects associated with decreased kidney energy generation, induced by kidney ablation, may result in an inability to control the body temperature.

Demonstration of intrinsic innervation of the guinea pig upper urinary tract using whole-mount preparation

AIMS

The morphology and functional importance of the autonomic nervous system in the upper urinary tract is still not completely understood. Previous histological studies investigating the innervation of the urinary tract have mainly used conventional sections in which the three-dimensional structure of the intramural innervation is difficult to achieve. In contrast, the whole-mount preparation technique is a suitable method for visualizing the distribution of the mesh-like neuronal networks within the urinary tract.

METHODS

The distribution and regional variation of neurofilament (NF), tyrosine hydroxylase (TH), choline acetyltransferase (ChAT), and substance P-immunoreactive (SP-IR) neurons, as well as acetylcholinesterase (AChE) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d)-positive neurons were investigated using whole-mount preparations of the guinea pig upper urinary tract.

RESULTS

Two distinct nervous plexuses were detected within the muscle layers containing NF, TH, ChAT, and SP-IR nerves. AChE-positive nerves were seen in all layers. Only moderate NADPH-d-positive innervation was found. Renal pelvis, upper and lower part of the ureter showed an overall increased innervation compared to the middle portion of the ureter. Ganglia were found at the pelviureteric border displaying NF and TH immunoreactivity.

CONCLUSION

The whole-mount preparation technique provides an elegant method for assessing the three-dimensional architecture of ureteral innervation. The guinea pig upper urinary tract is richly supplied with adrenergic, cholinergic, nitrergic, and sensory nerves which suggest that the autonomous nervous system plays an important role in controlling ureteral motility and blood flow.

Expression and localization of NK(1)R, substance P and CGRP are altered in dorsal root ganglia neurons of spontaneously hypertensive rats (SHR)

The kidneys play a pivotal role in the pathogenesis of essential hypertension because of a primary defect in renal hemodynamics and/or tubule hydro-saline handling that results in the retention of fluid and electrolytes. Previous studies have shown that increasing the renal pelvic pressure increased ipsilateral afferent renal nerve activity (ARNA), the ipsilateral renal pelvic release of substance P (SP) and the contralateral urinary sodium excretion in Wistar--Kyoto rats (WKy). However, spontaneously hypertensive rats (SHR) present an impaired renorenal reflex activity associated, partly, with a peripheral defect at the level of the sensory receptors in the renal pelvis. Furthermore, the renal pelvic administration of SP failed to increase ARNA in most of SHR at concentrations that produced marked increases in WKy. Since we have assessed the expression and localization of NK(1) receptor (NK(1)R), SP and calcitonin gene-related peptide (CGRP) in different dorsal root ganglia (DRG) cell subtypes and renal pelvis of 7- and 14-week-old SHR. The results of this study show increased SP and CGRP expression in the dorsal ganglia root cells of SHR compared to WKy rats. Additionally, there was a progressive, significant, age-dependent, decrease in NK(1)R expression on the membrane surface in SHR DRG cells and in the renal pelvis. In conclusion, the results of the present study suggest that the impaired activation of renal sensory neurons in SHR may be related to changes in the expression of neuropeptides and/or to a decreased presence of NK(1)R in DRG cells. Such abnormalities could contribute to the enhanced sodium retention and elevation of blood pressure seen in SHR.

Diuresis and Natriuresis Caused by Activation of VR1-Positive Sensory Nerves in Renal Pelvis of Rats

To test the hypothesis that activation of the vanilloid receptor 1 (VR1) expressed in sensory nerves innervating the renal pelvis leads to diuresis and natriuresis, a selective VR1 receptor agonist, capsaicin (2.4 nmol), or vehicle was perfused intravenously or into the left renal pelvis of anesthetized rats at a rate without changing renal perfusion pressure. Mean arterial pressure was not altered by capsaicin administered intravenously or into the renal pelvis. Capsaicin perfusion into the left renal pelvis but not intravenously caused significant increases in urine flow rate and urinary sodium excretion bilaterally in a dose-dependent manner, which were abolished by capsazepine, a selective VR1 receptor antagonist, given ipsilaterally to the renal pelvis or by ipsilateral renal denervation. Capsaicin given intravenously or into the left renal pelvis increased plasma calcitonin gene-related peptide levels to the same extent. Increased plasma calcitonin gene-related peptide levels induced by capsaicin (68.9±2.8 pg/mL) perfusion into the renal pelvis was prevented either by capsazepine (22.5±10.1 pg/mL) given ipsilaterally into the renal pelvis or by ipsilateral renal denervation (25.9±2.3 pg/mL). Taken together, our data show that unilateral activation of VR1-positive sensory nerves innervating the renal pelvis leads to bilateral diuresis and natriuresis via a mechanism that is independent of plasma calcitonin gene-related peptide levels. These data suggest that VR1-positive sensory nerves in the kidney enhance renal excretory function, a mechanism that may be critically involved in sodium and fluid homeostasis.

Activation of renal pelvic chemoreceptors in rats: role of calcitonin gene-related peptide receptors

Substance P and calcitonin gene-related peptide (CGRP) increase afferent renal nerve activity (ARNA). A substance P receptor antagonist but not a CGRP receptor antagonist, h-CGRP (8-37), blocks the ARNA response to renal mechanoreceptor (MR) stimulation. We have examined whether calcitonin gene-related peptide activates renal pelvic sensory receptors and whether such activation contributes to renal chemoreceptor stimulation. The calcitonin gene-related peptide receptor antagonist, h-CGRP (8-37) [0.01-10 micromol L-1] dose-dependently decreased (29 +/- 4-86 +/- 13%, P < 0.01) the ipsilateral afferent renal nerve activity in response to the renal pelvic administration of calcitonin gene-related peptide (0.26 micromol L-1). Renal pelvic perfusion with 900 mM NaCl also increased ipsilateral ARNA (23 +/- 3% increase, P < 0.02) and contralateral urinary sodium excretion (13 +/- 4% increase, P < 0. 05). However, these responses to hypertonic NaCl were unaltered by h-CGRP (8-37). Renal pelvic perfusion with 1 or 10 microM h-CGRP (8-37) also failed to alter the ARNA responses to KCl (31.25, 62.5 and 125 mM). These results indicate that there are sensory receptors in the renal pelvic area that are responsive to calcitonin gene-related peptide. The activation of these receptors elicits a contralateral natriuretic response. In contrast, the activation of renal calcitonin gene-related peptide receptors does not contribute to renal chemoreceptor activation.

CGRP activates renal pelvic substance P receptors by retarding substance P metabolism

Substance P and calcitonin gene-related peptide (CGRP) are colocalized in renal pelvic sensory nerves. Increasing renal pelvic pressure results in an increase in afferent renal nerve activity that is blocked by a substance P receptor antagonist but not by a CGRP receptor antagonist. CGRP potentiates the effects of substance P by preventing the metabolism of substance P. Therefore, we examined whether CGRP enhanced the afferent renal nerve activity responses to substance P and increased renal pelvic pressure, a stimulus known to increase substance P release. Combined administration of substance P and CGRP into the renal pelvis resulted in an increase in afferent renal nerve activity (1392+/-217%. s; area under the curve of afferent renal nerve activity versus time) that was greater (P<0.01) than that produced by substance P (620+/-156%. s) or CGRP (297+/-96%. s) alone. Likewise, CGRP enhanced the afferent renal nerve activity response to increased renal pelvic pressure. During renal pelvic administration of the neutral endopeptidase inhibitor thiorphan, the afferent renal nerve activity response to substance P plus CGRP was similar to that produced by either neuropeptide alone. Because these studies suggested that CGRP potentiated the afferent renal nerve activity responses to substance P, we examined whether the afferent renal nerve activity response to CGRP was blocked by a substance P receptor antagonist, RP67580. RP67580 blocked the afferent renal nerve activity response to CGRP by 85+/-12% (P<0.02). We conclude that CGRP activates renal pelvic sensory nerves by retarding the metabolism of substance P, thereby increasing the amount of substance P available for stimulation of substance P receptors.