Renal denervation regulates the atrial arrhythmogenic substrates through reverse structural remodeling in heart failure rabbit model.

BACKGROUND: Heart failure (HF) causes atrial remodeling and increases the incidence of atrial fibrillation (AF). Renal denervation (RDN) has been shown to decrease the development of AF. This study aimed to identify the effects of RDN on the atrial arrhythmogenic substrates in HF. METHODS: Rabbits were classified into four groups: control (n=9), RDN (n=10), HF (n=6) and HF-RDN (n=9). Surgical and chemical RDN was approached through bilateral retroperitoneal flank incisions in RDN and HF-RDN. Rapid ventricular pacing of 400bpm for 4weeks was applied in HF and HF-RDN. After 4weeks, the rabbits were sacrificed and atrial myocardium were harvested for Western blot and Trichrome stain. RESULTS: The bi-atrial effective refractory period (ERP) of HF was significantly longer compared with that of control and RDN. In right atrium, the ERP of HF was also significantly longer compared with that of HF-RDN, but there was no significant difference in left atrial ERP. In bi-atrium, ion channel protein expressions of CaV1.2, NaV1.5, Kir2.1 SERCA2 and NCX were similar among 4 groups. However, the degree of atrial fibrosis was extensive in bi-atrium of HF, when compared to that of control, RDN and HF-RDN. CONCLUSION: The ERP of HF-RDN is partially shortened by RDN compared with that of HF. There are no differences ionic channel protein expressions in bi-atrium among all groups. The degree of atrial fibrosis is severe in HF, but not in HF-RDN, suggesting that RDN may regulate the atrial arrhythmogenic substrates in HF mostly through reverse structural remodeling.

Carotid sinus denervation ameliorates renovascular hypertension in adult Wistar rats.

KEY POINTS: Peripheral chemoreflex sensitization is a feature of renovascular hypertension. Carotid sinus nerve denervation (CSD) has recently been shown to relieve hypertension and reduce sympathetic activity in other rat models of hypertension. We show that CSD in renovascular hypertension halts further increases in blood pressure. Possible mechanisms include improvements in baroreceptor reflex sensitivity and renal function, restoration of cardiac calcium signalling towards control levels, and reduced neural inflammation. Our data suggest that the peripheral chemoreflex may be a viable therapeutic target for renovascular hypertension. ABSTRACT: The peripheral chemoreflex is known to be hyper-responsive in both spontaneously hypertensive (SHR) and Goldblatt hypertensive (two kidney one clip; 2K1C) rats. We have previously shown that carotid sinus nerve denervation (CSD) reduces arterial blood pressure (ABP) in SHR. In the present study, we show that CSD ameliorates 2K1C hypertension and reveal the potential underlying mechanisms. Adult Wistar rats were instrumented to record ABP via telemetry, and then underwent CSD (n = 9) or sham CSD (n = 9) 5 weeks after renal artery clipping, in comparison with normal Wistar rats (n = 5). After 21 days, renal function was assessed, and tissue was collected to assess sympathetic postganglionic intracellular calcium transients ([Ca2+ ]i ) and immune cell infiltrates. Hypertensive 2K1C rats showed a profound elevation in ABP (Wistar: 98 ± 4 mmHg vs. 2K1C: 147 ± 8 mmHg; P < 0.001), coupled with impairments in renal function and baroreflex sensitivity, increased neuroinflammatory markers and enhanced [Ca2+ ]I in stellate neurons (P < 0.05). CSD reduced ABP in 2K1C+CSD rats and prevented the further progressive increase in ABP seen in 2K1C+sham CSD rats, with a between-group difference of 14 ± 2 mmHg by week 3 (P < 0.01), which was accompanied by improvements in both baroreflex control and spectral indicators of cardiac sympatho-vagal balance. Furthermore, CSD improved protein and albuminuria, decreased [Ca2+ ]i evoked responses from stellate neurons, and also reduced indicators of brainstem inflammation. In summary, CSD in 2K1C rats reduces the hypertensive burden and improves renal function. This may be mediated by improvements in autonomic balance, functional remodelling of post-ganglionic neurons and reduced inflammation. Our results suggest that the peripheral chemoreflex may be considered as a potential therapeutic target for controlling renovascular hypertension.

The effect of percutaneous renal denervation on muscle sympathetic nerve activity in hypertensive patients.

OBJECTIVE: The rationale of percutaneous renal denervation (RDN) is based on extensive studies suggesting that renal nerves contribute to hypertension and that they comprise a sensible treatment target. Muscle sympathetic nerve activity (MSNA) is considered to be one of the few reliable methods to quantify central sympathetic activity. The aim of this current study is to determine the effect of RDN on MSNA in a standardized fashion. METHODS: MSNA was determined in 13 patients before and 6months after RDN. Anti-hypertensive medication was stopped before MSNA. If cessation of medication was considered unsafe, a patient was instructed to use the exact same medication on both occasions. RESULTS: Ten sets of MSNA recordings were of good quality for analysis. Mean age was 57 ± 3 years and mean eGFR was 85 ± 18 mL/min/1.73 m(2). MSNA was determined twice during a medication free interval in 5 patients; 1 patient used the exact same medication twice, and 4 patients used different drugs. Mean BP changed from 206 ± 7 over 116 ± 4 mmHg, to 186 ± 6 over 106 ± 3 mmHg, 6 months after RDN (p=0.06 for systolic BP, p=0.04 for diastolic BP). Mean resting heart rate did not change (p=0.44). MSNA did not change after RDN: 37 ± 4 bursts/min and 43 ± 4 bursts/min (p=0.11) at baseline and after RDN, respectively. In the 6 patients with standardized medication use during the MSNA sessions, results were comparable. CONCLUSIONS: Treatment with RDN did not result in a change in MSNA. Changes in BP did not correlate with changes in MSNA.

VEGF promotes vascular sympathetic innervation.

The sympathetic nervous system, via postganglionic innervation of blood vessels and the heart, is an important determinant of cardiovascular function. The mechanisms underlying sympathetic innervation of targets are not fully understood. This study tests the hypothesis that target-derived vascular endothelial growth factor (VEGF) promotes sympathetic innervation of blood vessels. Western blot and immunohistochemical analyses indicate that VEGF is produced by vascular cells in arteries and that VEGF receptors are expressed on sympathetic nerve fibers innervating arteries. In vitro, exogenously added VEGF and VEGF produced by vascular smooth muscle cells (VSMCs) in sympathetic neurovascular cocultures inhibited semaphorin 3A (Sema3A)-induced collapse of sympathetic growth cones. In the absence of Sema3A, VEGF and VSMCs also increased growth cone area. These effects were mediated via VEGF receptor 1. In vivo, the neutralization of VEGF inhibited the reinnervation of denervated femoral arteries. These data demonstrate that target-derived VEGF plays a previously unrecognized role in promoting the growth of sympathetic axons.

Hepatic blood flow responses to mechanical stimulation of the skin in anaesthetised rats.

The aim of the present study was to investigate how hepatic blood flow (HBF) changes in response to mechanical stimulation of different areas of the skin in anaesthetised rats, by focusing on involvement of the hepatic sympathetic nerves in and contribution of systemic circulatory changes to the HBF responses. HBF was measured at the surface of the left lateral lobe using the laser Doppler flowmetry. Both innocuous and noxious mechanical stimuli were applied to skin areas of the abdomen and hindlimb. Innocuous mechanical stimulation (brushing) of the abdomen and hindlimb did not significantly change HBF, while noxious mechanical stimulation (pinching) of the abdomen and hindlimb did. The responses to pinching were dependent on the sites stimulated. Pinching of the abdomen decreased, while pinching of the hindlimb increased the HBF. The decrease of HBF in response to abdominal pinching remained after the spinal cord was transected at T1-2 level, but the response was diminished after hepatic sympathetic nerves were severed. On the other hand, the increase of HBF in response to hindlimb pinching was dependent on the increase in blood pressure, and was not influenced by the severance of hepatic sympathetic nerves, and the responses to hindlimb pinching were almost absent after the spinal cord was transected. Based on these results, we suggest that noxious mechanical stimulation of the skin produces changes of HBF, either as a reflex response via activation of the hepatic sympathetic nerves or as a passive response to systemic circulatory changes, depending on the sites stimulated.

Novel method for localized, functional sympathetic nervous system denervation of peripheral tissue using guanethidine.

A simple technique for local chemical sympathectomy of peripheral tissues is described using guanethidine. Multiple microinjections of guanethidine were made into inguinal or epididymal white adipose tissue (IWAT and EWAT) pads or spleens of hamsters. Guanethidine virtually abolished the sympathetic innervation of both EWAT and IWAT, as measured by the absence of significant norepinephrine (NE) tissue content two weeks later and as suggested by the two-fold increase in IWAT mass characteristic of surgically induced WAT denervation. These measures were not affected in the contralateral pads given equivolumetric injections of saline. Guanethidine injections into the spleen lead to a functional sympathectomy, as indicated by significant depletions of NE content. Because guanethidine treatment did not decrease body mass, induce ptosis, or spread to closely associated adjacent tissue (contralateral EWAT pad), no chemical-induced malaise or global sympathetic denervation was suggested. Guanethidine was more effective than two other local sympathectomy treatments, injections of the sympathetic neurotoxin anti-dopamine-beta-hydroxylase saporin or surgical denervation, in decreasing IWAT NE content and increasing IWAT pad mass. Collectively, these results suggest that locally applied, chemical sympathectomy with guanethidine provides an effective, restricted method for sympathectomizing WAT, spleen and likely other peripheral tissues.

In vivo observation of a non-noradrenergic regulation of arylalkylamine N-acetyltransferase gene expression in the rat pineal complex.

The rodent pineal gland is the end point of several peripheral and central fibers innervating the superficial and deep parts of the gland. Up to now, only the sympathetic transmitter norepinephrine is thought to regulate melatonin synthesis, although numerous biochemical experiments have reported in vitro effects of various transmitters on melatonin synthesis. To find out whether there is non-noradrenergic regulation of in vivo pineal metabolism, the mRNA encoding the enzyme arylalkylamine N-acetyltransferase was studied using the highly sensitive technique of in situ hybridization. The existence of a marked nocturnal increase of arylalkylamine N-acetyltransferase mRNA in the superficial pineal gland was confirmed. Interestingly and for the first time, a similar daily variation was observed in the deep pineal. After removal of superior cervical ganglia, the daily rhythm in arylalkylamine N-acetyltransferase mRNA was abolished in both the superficial and deep pineal indicating that the rhythm is driven by sympathetic input in the entire pineal complex. Interestingly, the remaining arylalkylamine N-acetyltransferase mRNA level in the pineal of day- and night-time ganglionectomized rats was significantly higher than in the pineal of day-time intact animals. These data reveal a sympathetic-dependent day-time inhibition of arylalkylamine N-acetyltransferase gene expression. In addition, the day-time pineal arylalkylamine N-acetyltransferase mRNA expression in ganglionectomized rats persisted after adrenal gland removal but was reduced by 50% after propranolol injection. These results indicate that arylalkylamine N-acetyltransferase mRNA in ganglionectomized rats is not induced by circulating catecholamines and may be caused by both a centrally originated norepinephrine, as already suggested, and other non-adrenergic transmitter(s). In conclusion, this work shows that norepinephrine drives the nocturnal increase of arylalkylamine N-acetyltransferase gene expression both in the superficial and deep pineal and strongly suggests that other neurotransmitters are involved in day-time inhibition and night-time stimulation of pineal metabolism.