Norepinephrine Spillover Research Articles

Reduced Cardiac Beta 1 Receptor Expression and Function in a Mouse Model of Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common genetic heart disorder. HCMis characterized by cardiac hypertrophy, fibrosis, and an increased risk of fatalarrhythmias and sudden cardiac death. Previous studies in humans with HCM havedemonstrated increased cardiac norepinephrine spillover and reduced beta-1 receptor(B1R) expression in the left ventricle (LV). We have previously demonstrated thatcardiac sympathetic tone is elevated in an alpha-tropomyosin mutant mouse model ofHCM. We hypothesized that HCM mice would demonstrate reduced B1R expression inthe LV and attenuated heart rate (HR) and dP/dt max responses to ramped infusion of theB1R agonist, dobutamine. First, we utilized western blot to measure B1R proteinexpression in LV tissue from HCM and littermate wild-type (WT) mice (n=4 male micein each group). B1R expression was significantly reduced in the LV of HCM micecompared to WT littermate controls (HCM 60±1% vs. WT 100±4%; paired t-test, p<0.05). Next, we recorded left ventricular pressure in male and female HCM andlittermate WT control (n=5 male mice, each group; n=6 female mice, each group) miceanesthetized with isoflurane (2% in O2). Data were analyzed by 2-way ANOVA withgenotype and sex as factors. Baseline HR and dP/dt max were significantly lower inHCM compared to WT mice (genotype p<0.05), however, there were no sex differencesin either variable (sex p>0.05). Next, in order to assess cardiac B1R function, we firstinfused the ganglionic blocker chlorisondamine (6ug/g) to eliminate autonomic reflexfunction in HCM and littermate WT mice (n=4 mice, each group). Then, we performed adobutamine stress test via ramped infusion of dobutamine starting at 2ng/g/min andincreasing the dose in 2ng/g/min increments every 2 minutes up to 12ng/g/min via aprogrammable syringe pump. Data were analyzed by 2-way ANOVA with dose andgenotype as factors. Contrary to our hypothesis, ramped infusion of dobutamine resultedin a similar, significant (dose p<0.05) increase in HR in both HCM and WT mice(genotype p>0.05). Peak increases in HR occurred during the highest dose ofdobutamine (12ng/g/min; ΔHR HCM 58±19 vs. WT 70±20 beats/min) in both groups.Consistent with our hypothesis, increases in dP/dt max were significantly blunted inHCM mice compared to littermate WT controls (dose x genotype p<0.05). Peakincreases in dP/dt max occurred at a lower dose of dobutamine for HCM (4ng/g/min;ΔdP/dt max 1129±767 mmHg/s) compared to WT (8ng/g/min; ΔdP/dt max 4882±499mmHg/s). In summary, LV B1R expression is reduced in HCM mice. Increases in HR inresponse to ramped infusion of dobutamine were similar between HCM and WT micewhereas increases in dP/dt max were attenuated in HCM mice. We speculate that thedifferential inotropic and chronotropic responses to dobutamine could be due to regionaldifferences in B1R expression or contractile dysfunction in HCM mice. Michigan Technological University Startup. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Acute isometric and dynamic exercise do not alter cerebral sympathetic nerve activity in healthy humans

The impact of physiological stressors on cerebral sympathetic nervous activity (SNA) remains controversial. We hypothesized that cerebral noradrenaline (NA) spillover, an index of cerebral SNA, would not change during both submaximal isometric handgrip (HG) exercise followed by a post-exercise circulatory occlusion (PECO), and supine dynamic cycling exercise. Twelve healthy participants (5 females) underwent simultaneous blood sampling from the right radial artery and right internal jugular vein. Right internal jugular vein blood flow was measured using Duplex ultrasound, and tritiated NA was infused through the participants' right superficial forearm vein. Heart rate was recorded via electrocardiogram and blood pressure was monitored using the right radial artery. Total NA spillover increased during HG (P = 0.049), PECO (P = 0.006), and moderate cycling exercise (P = 0.03) compared to rest. Cerebral NA spillover remained unchanged during isometric HG exercise (P = 0.36), PECO after the isometric HG exercise (P = 0.45), and during moderate cycling exercise (P = 0.94) compared to rest. These results indicate that transient increases in blood pressure during acute exercise involving both small and large muscle mass do not engage cerebral SNA in healthy humans. Our findings suggest that cerebral SNA may be non-obligatory for exercise-related cerebrovascular adjustments.

Gut microbial DNA and immune checkpoint gene Vsig4/CRIg are key antagonistic players in healthy aging and age-associated development of hypertension and diabetes.

Aging is associated with the development of insulin resistance and hypertension which may stem from inflammation induced by accumulation of toxic bacterial DNA crossing the gut barrier. The aim of this study was to identify factors counter-regulating these processes. Taking advantage of the Chromogranin A (CgA) knockout (CgA-KO) mouse as a model for healthy aging, we have identified Vsig4 (V-set and immunoglobulin domain containing 4) as the critical checkpoint gene in offsetting age-associated hypertension and diabetes. The CgA-KO mice display two opposite aging phenotypes: hypertension but heightened insulin sensitivity at young age, whereas the blood pressure normalizes at older age and insulin sensitivity further improves. In comparison, aging WT mice gradually lost glucose tolerance and insulin sensitivity and developed hypertension. The gut barrier, compromised in aging WT mice, was preserved in CgA KO mice leading to major 35-fold protection against bacterial DNA-induced inflammation. Similarly, RNA sequencing showed increased expression of the Vsig4 gene (which removes bacterial DNA) in the liver of 2-yr-old CgA-KO mice, which may account for the very low accumulation of microbial DNA in the heart. The reversal of hypertension in aging CgA-KO mice likely stems from (i) low accumulation of microbial DNA, (ii) decreased spillover of norepinephrine in the heart and kidneys, and (iii) reduced inflammation. We conclude that healthy aging relies on protection from bacterial DNA and the consequent low inflammation afforded by CgA-KO. Vsig4 also plays a crucial role in "healthy aging" by counteracting age-associated insulin resistance and hypertension.

Factors Influencing Muscle Sympathetic Nerve Activity in Human Heart Failure

In heart failure (HF), the magnitude of sympathetic activation predicts both disease progression and mortality. Elevated cardiac norepinephrine (NE) spillover is the earliest documented perturbation, followed later by augmented renal NE spillover and muscle sympathetic nerve activity (MSNA). To date, there is limited understanding of the mechanism(s) responsible for between‐patient variation in MSNA and cohorts studied have been small. To characterize the magnitude of MSNA discharge in HF, its inter‐patient variance, and its principal determinants, we assembled microneurographic data from 177 HF patients (28 females; 53±13 yr; LVEF: 25±11%, range 5‐60%) studied in our laboratory. Data from 658 non‐medicated, normotensive volunteers (CTRL; 260 females; 53±14 yr) acquired contemporaneously under similar conditions served as a reference group. We analyzed, at rest, fibular MSNA, blood pressure (BP), heart rate (HR), LVEF, and etiology of disease, and in a sub‐group (n=63), echocardiographically‐derived stroke volume (SV), cardiac output (CO), and total peripheral resistance (TPR). In HF, there was marked inter‐patient variance in MSNA, with burst frequency (BF) ranging from 7 to 90 bursts/minandburst incidence (BI) from 9 to 100 bursts/100 heartbeats. BF was similar in patients dispensed or not dispensed each of the three principal classes of prevailing HF therapy (all P>0.05). BF related directly (R2=0.17), and BI inversely (R2=0.09), to HR (all P<0.001); neither correlated with BP. For each kg/m2 rise in BMI, BF increased, on average, by 0.20 bursts/min (95% CI, 0.02‐0.37; P=0.03); its relation to BI was less pronounced (P=0.05). BF increased non‐linearly when LVEF fell below ~21% (P<0.01); above this inflection point, BF displayed no relationship with LVEF. Overall, LVEF accounted for only 9.8% of the variance in BF (P=0.001), while no relationship existed between LVEF and BI (R2=0.007). BI (P=0.01), but not BF (P=0.14), was greater in patients with ischemic vs. dilated cardiomyopathy. BF and BI exhibited non‐linear, inverse relationships with SV (R2=0.31 and 0.12; all P<0.01) and CO (R2=0.17 and 0.20; all P<0.01), and a non‐linear, direct relationship with TPR (R2=0.18 and 0.21; all P<0.01). Unadjusted BF (52±15 vs. 26±13 bursts/min; P<0.001) was elevated in HF vs. CTRL. With age, BF exhibited little or no change in HF, in contrast to its non‐linear increase in CTRL. BF, adjusted for age, sex, BMI, and HR, was significantly greater throughout the lifespan (estimate 14.20 bursts/min; 95% CI, 12.11‐16.28; P<0.001) in HF, relative to CTRL, and higher in men than in women (estimate 5.01 bursts/min; 95% CI, 3.42‐6.61; P<0.001). Overall, the extent of sympathetic excess in HF, relative to CTRL, diminished with age. In conclusion, resting MSNA in HF is a function of etiology, BMI, HR, LVEF and SV, but not age; these relationships are significant but moderate to weak, as is that between sympathetic vasoconstrictor discharge and TPR. These observations provide insight into the complexity and individual specificity of mechanisms eliciting muscle sympathetic excitation in human HF.

Renal Deafferentation Prevents Progression of Hypertension and Changes to Sympathetic Reflexes in a Rabbit Model of Chronic Kidney Disease.

[Figure: see text].

The Sympathetic Nervous System in Hypertension: Roadmap Update of a Long Journey.

The present paper will provide an update on the role of sympathetic neural factors in the development and progression of essential hypertension by reviewing data collected in the past 10 years. This will be done by discussing the results of the published studies in which sympathetic neural function in essential hypertension and related disease has been investigated via sophisticated and highly sensitive techniques, such as microneurographic recording of sympathetic nerve traffic and regional norepinephrine spillover. First, the relevance of the pathophysiological background of the neurogenic alterations will be discussed. It will be then examined the behavior of the sympathetic neural function in specific clinical phenotypes, such as resistant hypertension, pseudoresistant hypertension, and hypertensive states displaying elevated resting heart values. This will be followed by a discussion of the main results of the meta-analytic studies examining the behavior of sympathetic nerve traffic in essential hypertension, obesity, metabolic syndrome, and chronic renal failure. The sympathetic effects of renal denervation and carotid baroreceptor stimulation as well as the possible involvement of sympathetic neural factors in the determination of the so-called “residual risk” of the treated hypertensive patients will be finally discussed.

A Retinoic Acid β 2‐Receptor Agonist Exerts Cardioprotective Effects

Metabolic syndrome and hyperlipidemia are causally associated with myocardial ischemia and oxidative stress. We have now investigated the effects of AC261066, a synthetic selective agonist for the retinoic acid β2-receptor, in an ex vivo ischemia/reperfusion (I/R) injury model in hearts using genetically hypercholesterolemic (ApoE-/-) and metabolic syndrome inducing high fat diet (HFD) fed wild-type mouse models. We found that a 6-week oral treatment with AC261066 in both models exerts protective effects when their hearts are subsequently subjected to I/R ex vivo in the absence of AC261066. In ApoE-/- mice this cardioprotection ensued without hyperlipidemic changes. Cardioprotection consisted of attenuation of infarct size, diminution of norepinephrine (NE) spillover, and alleviation of reperfusion arrhythmias. This cardioprotection was associated with a reduction in oxidative stress and mast cell (MC) degranulation. We suggest that the reduction in myocardial injury and adrenergic activation, and the antiarrhythmic effects, result from decreased formation of oxygen radicals and toxic aldehydes that is known to elicit the release of MC-derived renin, promote the local renin-angiotensin system activation that enhances NE release, and reperfusion arrhythmias. Because these beneficial effects of AC261066 occurred at the ex vivo level following oral drug treatment, our data suggest that AC261066 could be viewed as a therapeutic means to reduce I/R injury of the heart, and potentially also be considered in the treatment of other cardiovascular ailments such as chronic arrhythmias and cardiac failure. Currently we are exploring the cardiac protective effects of AC261066 using an in vivo heart failure model.

MODULATION OF SYMPATHETIC NERVE ACTIVITY BY SGLT2 INHIBITOR EMPAGLIFLOZIN IN DIABETIC RABBITS

Objective: Treatment with the sodium-glucose cotransporter 2 (SGLT2) inhibitor empagliflozin in patients with type-2 diabetes is associated with 38% reduction in cardiovascular mortality. We explored the notion that the mechanisms underlying these benefits may involve an action on the sympathetic nervous system (SNS). Design and method: Diabetes was induced by alloxan in New-Zealand White rabbits. We determined the associated changes in blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) as well as baroreflex responses to changes in BP and norepinephrine spillover in conscious rabbits. The effects of one-week treatment with empagliflozin were compared to those of another blood glucose-lowering treatment insulin, the proximally-acting natriuretic acetazolamide, the ACE inhibitor perindopril, vehicle treatment and to an untreated diabetic group. Results: Diabetic rabbits were treated with daily insulin to maintain a stable elevation in blood glucose over 4 weeks (20.5 ± 0.4 mM vs 6.5 ± 0.4 mM in controls). BP was 9% greater in diabetic than non-diabetic rabbits (P = 0.02) but there were no differences in RSNA or HR. One-week treatment with empagliflozin (without insulin) lowered blood glucose by 43% but there was no difference in BP, HR or RSNA between these animals and untreated diabetic rabbits or those treated with acetazolamide. However, insulin treatment alone lowered blood glucose similarly to empagliflozin (32%) and increased HR (+10%) while perindopril lowered BP (-9%). In diabetic rabbits there was marked augmentation of the maximum RSNA response to baroreceptor unloading compared to non-diabetic (+69%, P < 0.01). Empagliflozin attenuated the baroreflex by 34% and there was a similar reduction after acetazolamide (-29%, both P < 0.05). Empagliflozin also attenuated the HR baroreflex (-8%) but insulin and perindopril had no effect on either baroreflex. Norepinephrine spillover to plasma was similar in diabetic and non-diabetic rabbits but was elevated after both empagliflozin and acetazolamide (+147% and + 134%, P < 0.05). Conclusions: Empagliflozin normalised the maximal RSNA response to lowering BP, which was exaggerated in diabetic rabbits, without altering BP or resting RSNA. A similar action of the natriuretic acetazolamide suggests that the mechanism underlying the cardiovascular benefits of empagliflozin may involve increased sodium and water excretion.

Contribution of the Renal Nerves to Hypertension in a Rabbit Model of Chronic Kidney Disease.

Overactivity of the sympathetic nervous system and high blood pressure are implicated in the development and progression of chronic kidney disease (CKD) and independently predict cardiovascular events in end-stage renal disease. To assess the role of renal nerves, we determined whether renal denervation (RDN) altered the hypertension and sympathoexcitation associated with a rabbit model of CKD. The model involves glomerular layer lesioning and uninephrectomy, resulting in renal function reduced by one-third and diuresis. After 3-week CKD, blood pressure was 13±2 mm Hg higher than at baseline (P<0.001), and compared with sham control rabbits, renal sympathetic nerve activity was 1.2±0.5 normalized units greater (P=0.01). The depressor response to ganglion blockade was also +8.0±3 mm Hg greater, but total norepinephrine spillover was 8.7±3.7 ng/min lower (both P<0.05). RDN CKD rabbits only increased blood pressure by 8.0±1.5 mm Hg. Renal sympathetic activity, the response to ganglion blockade and diuresis were similar to sham denervated rabbits (non-CKD). CKD rabbits had intact renal sympathetic baroreflex gain and range, as well as normal sympathetic responses to airjet stress. However, hypoxia-induced sympathoexcitation was reduced by -9±0.4 normalized units. RDN did not alter the sympathetic response to hypoxia or airjet stress. CKD increased oxidative stress markers Nox5 and MCP-1 (monocyte chemoattractant protein-1) in the kidney, but RDN had no effect on these measures. Thus, RDN is an effective treatment for hypertension in this model of CKD without further impairing renal function or altering the normal sympathetic reflex responses to various environmental stimuli.

Cardiovascular Manifestations and Complications of Pheochromocytomas and Paragangliomas.

Pheochromocytomas and paragangliomas (PPGLs) are rare neuro-endocrine tumors. The catecholamine surge causes paroxysmal or chronic secondary hypertension. PPGLs may present as hypertensive- or PPGL-crisis with severe life-threatening cardiac and cerebrovascular complications. PPGLs-induced cardiac manifestations have been reported with diagnoses as PPGLs-induced electrocardiogram (ECG) changes “mimicking acute myocardial infarction”, arrhythmias, myocarditis, acute coronary syndrome, dilated cardiomyopathy, and lately as takotsubo syndrome. Critical analysis of these reports reveals that most of these cardiac manifestations have certain features in common. They have a dramatic clinical presentation and are reversible if the disease is treated with appropriate medical therapy and surgical resection of the PPGL tumor. They may have the same repolarization ECG changes irrespective of the clinical cardiac diagnosis, usually associated with mild to moderate elevations of myocardial biomarkers as troponins and normal coronary arteries. The histopathological findings are usually focal or multifocal in the form hypercontracted sarcomeres and contraction band necrosis (myofibrillar degeneration) with subsequent secondary mononuclear cell infiltration. Evidences argue the PPGL caused surge of catecholamines triggers hyperactivation of the sympathetic nervous system with cardiac sympathetic nerve terminal disruption with norepinephrine spillover causing the cardiac complications. A comprehensive review of various reported cardiovascular manifestations and complications of PPGLs are presented.

Autonomic neurocardiogenic syndrome is stonewalled by the universal definition of myocardial infarction.

Myocardial infarction (MI) is defined as myocardial cell death due to prolonged myocardial ischemia. Clinically, troponin rise and/or fall have become the “defining feature of MI” according to the universal definition of MI (UD-MI). Takotsubo syndrome (TS) and TS-related disease conditions also cause troponin elevation with typical rise and/or fall pattern but through a mechanism other than coronary ischemia. By strict application of the clinical diagnostic criteria for type-1 MI, type-2 MI, type-3 MI, and MI with non-obstructive coronary arteries according to the UD-MI including the fourth one published recently, TS and most of the 26 other causes of troponin elevation mentioned in the fourth UD-MI may erroneously be classified as MI. The existing evidence argues for the case that TS by itself is not a MI. Hyper-activation of the autonomic-sympathetic nervous system including local cardiac sympathetic hyper-activation and disruption with nor-epinephrine churn and spillover is the most probable cause of TS. This autonomic neuro-cardiogenic (ANCA) mechanism results in myocardial “cramp” (stunning), the severity and duration of which depend on the degree of the sympathetic-hyperactivation and nor-epinephrine spillover. The myocardial cramp may squeeze the cytosolic free troponin pools causing mild to moderate troponin elevation in TS and TS-related disease conditions. This ANCA syndrome, which has hitherto been enveloped by the UD-MI over more than one decade, may occur in acute, recurrent, and chronic forms. In this critical review, the controversies of UD-MI, evidence for ANCA syndrome, and a hypothetical mechanism for the troponin elevation in ANCA syndrome are provided.

Empagliflozin modulates renal sympathetic and heart rate baroreflexes in a rabbit model of diabetes.

We determined whether empagliflozin altered renal sympathetic nerve activity (RSNA) and baroreflexes in a diabetes model in conscious rabbits. Diabetes was induced by alloxan, and RSNA, mean arterial pressure (MAP) and heart rate were measured before and after 1week of treatment with empagliflozin, insulin, the diuretic acetazolamide or the ACE inhibitor perindopril, or no treatment, in conscious rabbits. Four weeks after alloxan administration, blood glucose was threefold and MAP 9% higher than non-diabetic controls (p < 0.05). One week of treatment with empagliflozin produced a stable fall in blood glucose (-43%) and increased water intake (+49%) but did not change RSNA, MAP or heart rate compared with untreated diabetic rabbits. The maximum RSNA to hypotension was augmented by 75% (p < 0.01) in diabetic rabbits but the heart rate baroreflex was unaltered. Empagliflozin and acetazolamide reduced the augmentation of the RSNA baroreflex (p < 0.05) to be similar to the non-diabetic group. Noradrenaline (norepinephrine) spillover was similar in untreated diabetic and non-diabetic rabbits but twofold greater in empagliflozin- and acetazolamide-treated rabbits (p < 0.05). As empagliflozin can restore diabetes-induced augmented sympathetic reflexes, this may be beneficial in diabetic patients. A similar action of the diuretic acetazolamide suggests that the mechanism may involve increased sodium and water excretion. Graphical abstract.

Differential sympathetic response to lesion-induced chronic kidney disease in rabbits

Chronic kidney disease (CKD) is associated with greater sympathetic nerve activity but it is unclear if this is a kidney-specific response or due to generalized stimulation of sympathetic nervous system activity. To determine this, we used a rabbit model of CKD in which quantitative comparisons with control rabbits could be made of kidney sympathetic nerve activity and whole-body norepinephrine spillover. Rabbits either had surgery to lesion 5/6th of the cortex of one kidney by electro-lesioning and two weeks later removal of the contralateral kidney, or sham lesioning and sham nephrectomy. After three weeks, the blood pressure was statistically significantly 20% higher in conscious rabbits with CKD compared to rabbits with a sham operation, but their heart rate was similar. Strikingly, kidney nerve activity was 37% greater than in controls, with greater burst height and frequency. Total norepinephrine spillover was statistically significantly lower by 34%, and kidney baroreflex curves were shifted to the right in rabbits with CKD. Plasma creatinine and urine output were elevated by 38% and 131%, respectively, and the glomerular filtration rate was 37% lower than in sham-operated animals (all statistically significant). Kidney gene expression of fibronectin, transforming growth factor-β, monocyte chemotactic protein1, Nox4 and Nox5 was two- to eight-fold greater in rabbits with CKD than in control rabbits. Overall, the glomerular layer lesioning model in conscious rabbits produced a moderate, stable degree of CKD characterized by elevated blood pressure and increased kidney sympathetic nerve activity. Thus, our findings, together with that of a reduction in total norepinephrine spillover, suggest that kidney denervation, rather than generalized sympatholytic treatments, may represent a preferable management for CKD associated hypertension.

Treatment with SGLT2 Inhibitor Empagliflozin Modulates Renal Sympathetic Nerve Activity in Diabetic Rabbits

In patients with type 2 diabetes, antihyperglycemic treatment with the sodium‐glucose cotransporter 2 (SGLT2) inhibitor empagliflozin is associated with a reduction in cardiovascular mortality of 38% (EMPA‐REG OUTCOME trial). In individuals with poorly controlled type 2 diabetes, sympathetic nervous system (SNS) activation is associated with poor cardiovascular outcomes. We explored the notion that the mechanisms underlying the cardiovascular benefits of empagliflozin treatment may involve an action on the SNS.Diabetes was induced by a single dose of alloxan in New Zealand White rabbits. We determined the changes in blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) as well as baroreflex responses to changes in BP and norepinephrine spillover in conscious rabbits. The effects of one‐week treatment with empagliflozin were compared to those of another blood glucose‐lowering treatment insulin, the proximally‐acting natriuretic acetazolamide, the ACE inhibitor perindopril, vehicle treatment and to an untreated diabetic group.Diabetic rabbits (n=39) were treated with daily insulin to maintain a stable elevation in blood glucose (20.5±0.4mM vs 6.5±0.4mM in controls) over 4 weeks. Diabetes was associated with 9% greater BP than in non‐diabetic rabbits (P=0.02) but no difference in RSNA or HR. One‐week treatment with empagliflozin lowered blood glucose by 43% (without insulin), and there was a 49% increase in water intake. There was no difference in BP, HR or RSNA between empagliflozin‐treated and untreated diabetic rabbits or those treated with acetazolamide. However, insulin lowered blood glucose similarly to empagliflozin (32%) and increased HR (+10%) while perindopril lowered BP (−9%). There was marked augmentation (+69%) of the maximum RSNA response to baroreceptor unloading in diabetic rabbits compared to non‐diabetic (P&lt;0.01). Empagliflozin attenuated the baroreflex by 34% and acetazolamide had a similar blunting effect (−29%, both P&lt;0.05). Empagliflozin also attenuated the HR baroreflex (−8%) but insulin and perindopril had no effect on either baroreflex. Diabetes did not alter BP or HR variability but empagliflozin and acetazolamide treatment increased mid frequency HR power. Norepinephrine spillover to plasma was similar in diabetic and non‐diabetic rabbits but was elevated after both empagliflozin (+147%) and acetazolamide (+134%, P&lt;0.05).In conclusion, empagliflozin effectively normalized the maximal RSNA response to acute BP lowering without altering resting hemodynamic or sympathetic activity in conscious diabetic rabbits. The similarity of these effects with those of acetazolamide suggests that the mechanism underlying the cardiovascular benefits of empagliflozin is linked to its natriuretic action.Support or Funding InformationThis work was supported by Boehringer Ingelheim.

Evaluation of elevated heart rate as a sympathetic nervous system biomarker in essential hypertension.

There is a need for an easily accessible biomarker of sympathetic nervous activation in essential hypertension, but none exists. Heart rate (HR) has been suggested, but requires validation, now doubly important as an elevated HR in hypertension has emerged as an independent cardiovascular risk factor. Isotope dilution methodology was used to measure total and regional noradrenaline spillover and adrenaline secretion rates in 30 patients with unmedicated essential hypertension and in a comparator group of 48 healthy participants with normal blood pressure. The particular interest was in the relationship of measured HR to cardiac noradrenaline spillover, the measure of cardiac sympathetic activity. Sympathetic activation was present in the patients with essential hypertension, evident in significantly increased mean cardiac, renal and total noradrenaline spillover rates. Adrenaline secretion was normal. HR in hypertension correlated directly with cardiac noradrenaline spillover (r = 0.82, P = 9.3 × 10), but not with renal noradrenaline spillover or adrenaline secretion. 67% of the variance in HR was attributable to differences in cardiac sympathetic activity. Among hypertensive patients there was no internal correlation between cardiac noradrenaline spillover, renal noradrenaline spillover and adrenaline secretion; the sympathetic activation commonly was not 'global'. In healthy participants HR did not correlate with measures of sympathetic activity or adrenaline secretion. When sympathetic activation exists in essential hypertension it is differentiated, not necessarily involving all sympathetic outflows. An elevated HR proved to be a biomarker of cardiac sympathetic activation but not activation of the renal sympathetic outflow. Identifying activation of the cardiac sympathetic outflow as the prime mechanism of hypertension tachycardia is relevant to therapies which should now be considered to minimize cardiovascular risk in this clinical setting. Is an elevated HR a valid biomarker of sympathetic activation in essential hypertension? Yes, but only for the cardiac sympathetic outflow. The unavoidable principle is that regional differentiation of sympathetic responses in essential hypertension means that no simple test can ever represent each and every sympathetic outflow.

Comparison of short-acting versus extended-release nifedipine: Effects on hemodynamics and sympathetic activity in patients with stable coronary artery disease

We investigated the impact of short-acting and extended release nifedipine on sympathetic activity using radiotracer methodology in patients with stable coronary artery disease in order to more accurately document the response of the sympathetic nervous system to different formulations of this dihydropyridine calcium channel antagonist. Participants were randomized to placebo, short-acting or extended release nifedipine for 7–10 days. On the final day, systemic blood pressure, cardiac filling pressures, cardiac output, plasma norepinephrine (NE) and total body NE spillover were measured at baseline (time 0) and repeated at intervals for 6 hours. There were no differences in baseline measures between groups. Following the morning dose of study medication there were no changes in hemodynamics or sympathetic activity in the placebo group. However, there was a significant fall in blood pressure and a significant increase in total body NE spillover in both nifedipine groups. Importantly, the increase in sympathetic activity in response to short-acting nifedipine began earlier (30 minutes) and was much greater than that observed in the extended release group, which occurred later (270 minutes). These findings confirm that sustained therapy with nifedipine is associated with activation of the sympathetic nervous system which is dependent on the pharmacokinetics of the formulation.

Liver sympathetic nerve activity and steatosis.

Liver sympathetic nerve activity and steatosis.

Neurohumoral interactions contributing to renal vasoconstriction and decreased renal blood flow in heart failure

In heart failure (HF), increases in renal sympathetic nerve activity (RSNA), renal norepinephrine spillover, and renin release cause renal vasoconstriction, which may contribute to the cardiorenal syndrome. To increase our understanding of the mechanisms causing renal vasoconstriction in HF, we investigated the interactions between the increased activity of the renal nerves and the renal release of norepinephrine and renin in an ovine pacing-induced model of HF compared with healthy sheep. In addition, we determined the level of renal angiotensin type-1 receptors and the renal vascular responsiveness to stimulation of the renal nerves and α1-adrenoceptors. In conscious sheep with mild HF (ejection fraction 35%-40%), renal blood flow (276 ± 13 to 185 ± 18 mL/min) and renal vascular conductance (3.8 ± 0.2 to 3.1 ± 0.2 mL·min-1·mmHg-1) were decreased compared with healthy sheep. There were increases in the burst frequency of RSNA (27%), renal norepinephrine spillover (377%), and plasma renin activity (141%), whereas the density of renal medullary angiotensin type-1 receptors decreased. In anesthetized sheep with HF, the renal vasoconstrictor responses to electrical stimulation of the renal nerves or to phenylephrine were attenuated. Irbesartan improved the responses to nerve stimulation, but not to phenylephrine, in HF and reduced the responses in normal sheep. In summary, in HF, the increases in renal norepinephrine spillover and plasma renin activity are augmented compared with the increase in RSNA. The vasoconstrictor effect of the increased renal norepinephrine and angiotensin II is offset by reduced levels of renal angiotensin type-1 receptors and reduced renal vasoconstrictor responsiveness to α1-adrenoceptor stimulation.

IGF-1 deletion affects renal sympathetic nerve activity, left ventricular dysfunction, and renal function in DOCA-salt hypertensive mice.

To determine the influence of IGF-1 deletion on renal sympathetic nerve activity (RSNA), left ventricular dysfunction, and renal function in deoxycorticosterone acetate (DOCA)-salt hypertensive mice. The DOCA-salt hypertensive mice models were constructed and the experiment was classified into WT (Wild-type mice) +sham, LID (Liver-specific IGF-1 deficient mice) + sham, WT + DOCA, and LID+ DOCA groups. Enzyme-linked immunosorbent assay (ELISA) was used to detect the serum IGF-1 levels in mice. The plasma norepinephrine (NE), urine protein, urea nitrogen and creatinine, as well as RSNA were measured. Echocardiography was performed to assess left ventricular dysfunction, and HE staining to observe the pathological changes in renal tissue of mice. DOCA-salt induction time-dependently increased the systolic blood pressure (SBP) of mice, especially in DOCA-salt LID mice. Besides, the serum IGF-1 levels in WT mice were decreased after DOCA-salt induction. In addition, the plasma NE concentration and NE spillover, urinary protein, urea nitrogen, creatinine and RSNA were remarkably elevated with severe left ventricular dysfunction, but the creatinine clearance was reduced in DOCA-salt mice, and these similar changes were obvious in DOCA-salt mice with IGF-1 deletion. Moreover, the DOCA-salt mice had tubular ectasia, glomerular fibrosis, interstitial cell infiltration, and increased arterial wall thickness, and the DOCA-salt LID mice were more serious in those aspects. Deletion of IGF-1 may lead to enhanced RSNA in DOCA-salt hypertensive mice, thereby further aggravating left ventricular dysfunction and renal damage.

IATROGENIC HEARTBREAK: STRESS CARDIOMYOPATHY AFTER ELECTRICAL CARDIOVERSION

Stress cardiomyopathy (SCM) causes transient left ventricular (LV) systolic dysfunction due to possible hyperactivation of a local sympathetic terminal with norepinephrine seethe and spillover. Direct current cardioversion (DCCV) for atrial fibrillation (A-fib) can rarely lead to LV dysfunction. 81