Infusion Of Nitroprusside Research Articles

Spontaneous Baroreflex Control of Muscle Sympathetic Nerve Activity in Humans: Standardizing Analysis Procedures

Beat‐to‐beat variations in muscle sympathetic nerve activity (MSNA) are strongly related to diastolic blood pressure (DBP) fluctuations, and the use of spontaneous occurring bursts of MSNA at rest to determine sympathetic baroreflex sensitivity has become more prevalent. However, published results using spontaneous sympathetic baroreflex sensitivity have lacked standard methodology for analysis. Indeed, there have been variations in the duration of the recording used, the size of the DBP bins (1‐, 2‐, 3‐mmHg), and strength of the linear regression r‐values accepted. Thus, we sought to comprehensively examine the influence of these varying analysis procedures on spontaneous sympathetic baroreflex sensitivity. Our goal was to provide a standardized procedure that would allow for consistent and comparable results across laboratories. In a collective group of subjects (n=150), weighted linear regression analysis between MSNA and DBP was performed with MSNA expressed as either burst incidence (bursts/100heartbeats) or total MSNA (summation of MSNA burst amplitude relative to number of cardiac cycles). Resting MSNA was analyzed over a 10‐min baseline period, and subsequently segregated into separate 5‐, 2‐, and 1‐min segments to examine the influence of baseline duration on the weighted linear regression. MSNA was averaged over 1‐, 2‐, or 3‐mmHg DBP ranges (bins) to examine the influence of bin size. Also, in a subset of subjects (n=35), the modified Oxford technique (intravenous infusion of sodium nitroprusside followed by phenylephrine) was performed for comparison. The average slope of the linear regressions for resting MSNA burst incidence and total MSNA progressively increased as the baseline duration decreased with 1‐min duration being significantly greater than 10 min (P<0.05); however, correlation coefficients were reduced with the shorter durations. Indeed, the 10‐min baseline durations most frequently yielded statistically significant probability values for linear regressions (P<0.05), which closely reflected the p‐values obtained during the modified Oxford. Interestingly, although bin size (1‐, 2‐, 3‐mmHg) had no major influence on the average slope of the regressions (P>0.05), correlation coefficients progressively increased with bin size such that the highest correlation coefficients were observed for the 3‐mmHg bin size for each time duration segment. Overall, the 10‐min durations and 3‐mmHg bin size yielded the highest correlation coefficients. Collectively, these findings suggest that the duration of the recording used for analysis impacts the statistical validity of the r‐values defining the slopes for spontaneous sympathetic baroreflex sensitivity, whereas larger bin size improves the r‐value but has less influence on the p‐value.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The role of striatum and prefrontal cortex in the prevention of amphetamine-induced schizophrenia-like effects mediated by nitric oxide compounds

Pharmacological manipulation of nitric oxide (NO) has been suggested as a promising treatment for schizophrenia symptoms. A single infusion of sodium nitroprusside, a NO donor with short half-life, was found to improve schizophrenia symptoms. However, an increasing number of preclinical studies have demonstrated the potential beneficial effects of both NO donors and inhibitors. We investigated the potential synergistic effect of sub-effective doses of the NO donor sodium nitroprusside or the NO inhibitor 7-Nitroindazole (7NI) combined with clozapine, a standard atypical antipsychotic, on counteracting amphetamine or MK-801-induced psychosis-like behaviors. The impact of sodium nitroprusside and 7NI on cAMP regulation in the prefrontal cortex and striatum was also evaluated. Confirming previous results, we found that both NO donors and inhibitors prevented amphetamine-induced effects (prepulse inhibition [PPI] disruption and hyperlocomotion). In addition, we observed a synergistic effect of sodium nitroprusside and clozapine on antagonizing the disruptive effects of amphetamine, but not MK-801, in the PPI test. The sub-effective dose of 7NI tested did not prevent amphetamine or MK-induced PPI effects when combined with clozapine. Interestingly, cAMP levels were significantly decreased in the prefrontal cortex after treatment with sodium nitroprusside. In the striatum, both sodium nitroprusside and 7NI blocked the amphetamine-induced increase of cAMP. Our data corroborate previous findings on the dopaminergic mechanisms involved in the action of sodium nitroprusside. It is likely that the differential effects of sodium nitroprusside are related to its ability to modify cAMP levels in the prefrontal cortex.

Neuroreflex control of cardiovascular function is impaired after acute poisoning with chlorpyrifos, an organophosphorus insecticide: Possible short and long term clinical implications

Although it is well-established that severe poisoning by organophosphorus (OP) compounds strongly affects the cardiorespiratory system, the effects of sub-lethal exposure to these compounds on the neural control of cardiovascular function are poorly explored. The aim of this study was to evaluate the effects of acute sub-lethal exposure to chlorpyrifos (CPF), a commonly used OP insecticide, on three basic reflex mechanisms involved in blood pressure regulation, the peripheral chemoreflex, the baroreflex and the Bezold-Jarisch reflex. Adult male Wistar rats were injected intraperitoneally with a single dose of CPF (30 mg/kg) or saline (0.9%). 24 h after injections, cardiovascular reflexes were tested in awake rats. Potassium cyanide (KCN) and phenylbiguanide (PBG) were injected intravenously to activate the chemoreflex and the Bezold-Jarisch reflex, respectively. The baroreflex was activated by phenylephrine and sodium nitroprusside infusions. Blood samples were taken for measurements of butyrylcholinesterase (BChE) activity while acetylcholinesterase (AChE) activity was measured in brainstem samples. Animals treated with CPF presented signs of intoxication such as ataxia, tremor, lacrimation, salivation, tetany, urination and defecation. The hypertensive and the bradycardic responses of the chemoreflex as well as the hypotensive and bradycardic responses of the Bezold-Jarisch reflex were attenuated in CPF treated animals (P < 0.05). Concerning the baroreflex responses, CPF treatment reduced the bradycardia plateau, the range and the gain of the reflex (P < 0.05). Plasma BChE and brainstem AChE were both reduced significantly after CPF treatment (P < 0.05). Our results showed that acute sub-lethal exposure to CPF impairs the cardiovascular responses of homeostatic and defensive cardiovascular reflexes. These effects are associated with a marked inhibition of plasma BChE and brainstem AChE.

Effects of sodium nitroprusside in the prevention of schizophrenia-like symptoms induced by ketamine – A translational double-blind study

Abstract Background: Recent evidence has shown improvements in schizophrenia symptoms after the infusion of sodium nitroprusside (SNP), a nitric oxide (NO) donor. In the rat model of schizophrenia using ketamine injection, pretreatment with SNP seems to prevent behavioral changes associated with positive symptoms for up to one week. Objective: We investigated whether SNP would have preventative effects on psychogenic symptoms induced by ketamine in healthy subjects. Methods: Healthy subjects (N = 38) were assigned to distinct groups that received SNP in different doses (0.15, 0.25, and 0.5 mcg/kg/min). First, participants received an infusion of SNP or placebo over 75 minutes. After 10 minutes, they were injected for 1 minute with a bolus of 0.26 mg/kg of ketamine and a maintenance dose was started 5 minutes later, with 0.25 mg/kg/h of ketamine for 50 minutes. Results: Ketamine-induced psychopathological alterations induced were reduced by SNP, as assessed with the Brief Psychological Rating Scale. Scores in the objective subscale of the Clinician-Administered Dissociative States Scale were also lower in SNP sessions compared to placebo. SNP had protective effects against deterioration in facial emotion and identity recognition tasks induced by ketamine. Discussion: Our findings support the view that SNP has preventative properties against psychotic manifestations.

Role of mitochondria-derived reactive oxygen species in microvascular dysfunction in chronic kidney disease.

Cardiovascular disease is the leading cause of mortality in chronic kidney disease (CKD). Mitochondrial dysfunction secondary to CKD is a potential source of oxidative stress that may impair vascular function. This study sought to determine if mitochondria-derived reactive oxygen species contribute to microvascular dysfunction in stage 3-5 CKD. Cutaneous vasodilation in response to local heating was assessed in 20 CKD patients [60 ± 13 yr; estimated glomerular filtration rate (eGFR) 46 ± 13 ml·kg-1·1.73 m-2] and 11 matched healthy participants (58 ± 2 yr; eGFR >90 ml·kg-1·1.73 m-2). Participants were instrumented with two microdialysis fibers for the delivery of 1) Ringer solution, and 2) the mitochondria- specific superoxide scavenger MitoTempo. Skin blood flow was measured via laser Doppler flowmetry during standardized local heating (42°C). Cutaneous vascular conductance (CVC) was calculated as a percentage of the maximum conductance achieved with sodium nitroprusside infusion at 43°C. Urinary isofuran/F2-isoprostane ratios were assessed by gas-chromatography mass spectroscopy. Isofuran-to-F2-isoprostane ratios were increased in CKD patients (3.08 ± 0.32 vs. 1.69 ± 0.12 arbitrary units; P < 0.01) indicative of mitochondria-derived oxidative stress. Cutaneous vasodilation was impaired in CKD compared with healthy controls (87 ± 1 vs. 92 ± 1%CVCmax; P < 0.01). Infusion of MitoTempo significantly increased the plateau phase CVC in CKD patients (CKD Ringer vs. CKD MitoTempo: 87 ± 1 vs. 93 ± 1%CVCmax; P < 0.01) to similar levels observed in healthy controls ( P = 0.9). These data provide in vivo evidence that mitochondria-derived reactive oxygen species contribute to microvascular dysfunction in CKD and suggest that mitochondrial dysfunction may be a potential therapeutic target to improve CKD-related vascular dysfunction.

Nebivolol, But Not Metoprolol, Treatment Improves Endothelial Fibrinolytic Capacity in Adults With Elevated Blood Pressure.

BackgroundVascular endothelial fibrinolytic function is impaired in adults with prehypertension and hypertension and plays a mechanistic role in the development of atherothrombotic events. The influence of β‐blockers on endothelial fibrinolysis is unknown. This study compared the effects of chronic nebivolol and metoprolol treatment on endothelial tissue‐type plasminogen activator (t‐PA) release in adults with elevated blood pressure (BP).Methods and ResultsForty‐four middle‐aged adults (36% women) with elevated BP completed a 3‐month, double‐blind, randomized, placebo‐controlled trial comparing nebivolol (5 mg/d), metoprolol succinate (100 mg/d), and placebo. Net endothelial t‐PA release was determined in vivo in response to intrabrachial infusions of bradykinin and sodium nitroprusside before and after each intervention. In a subset, the dose‐response curves to bradykinin and sodium nitroprusside were repeated with a coinfusion of the antioxidant vitamin C. At baseline, resting BP and endothelial t‐PA release were comparable between the 3 groups. BP decreased to a similar extent (≈10 mm Hg) in the nebivolol‐ and metoprolol‐treated groups. There was a substantial increase (≈30%; P<0.05) in the capacity of the endothelium to release t‐PA following chronic treatment with nebivolol but not metoprolol or placebo. Mitigating oxidant stress with vitamin C coinfusion potentiated t‐PA release (90%; P<0.05) at baseline in all groups. However, after the intervention, t‐PA release was unchanged by vitamin C coinfusion in the nebivolol group only.ConclusionsNebivolol but not metoprolol improves endothelial t‐PA release in adults with elevated BP. This may be an important vascular benefit of nebivolol.Clinical Trial Registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT01595516.

Abstract P183: Influence of Insufficient Sleep on Endothelial Fibrinolytic Capacity in Adults With Elevated Blood Pressure

The capacity of the endothelium to release tissue-type plasminogen activator (t-PA) is impaired in adults with elevated BP, leading to an increased risk of thrombotic events. Insufficient sleep is independently associated with elevated BP and impaired t-PA release. However, the compounded influence of insufficient sleep on t-PA release in adults with elevated BP is unknown. We tested the hypothesis that impairments in the capacity of the endothelium to release t-PA in adults with elevated BP is worse in those who sleep &lt;7 h/night (short sleep duration) compared with those who sleep 7 to 9 h/night (normal sleep duration). We studied 38 sedentary, middle-aged adults: 10 with normal BP and normal nightly sleep duration (6M/4F; age: 55±2 yr; BP: 114/94±2/3 mmHg, sleep duration: 7.4±0.2 h); 14 with elevated BP and normal nightly sleep duration (8M/6F; 60±2 yr; 141/87±2/2 mmHg; 7.8±0.1 h); and 14 with elevated BP and short nightly sleep duration (10M/4F; 57±2 yr; 139/85±2/2 mmHg; 6.1±0.2 h). All subjects were free of overt metabolic and coronary disease. Net endothelial release of t-PA was determined, in vivo, in response to intra-brachial infusions of bradykinin (BK: 125-500 ng/min) and sodium nitroprusside (SNP: 2.0-8.0 μg/min). In the normal sleep groups, as expected, endothelial t-PA release in response to BK was significantly blunted (~30%) in the adults with elevated BP (from -1.2±0.8 to 50.2±4.8 ng/100mL tissue/min) compared with normal BP (from 0.9±3.4 to 73.0±8.0 ng/100mL tissue/min); and total t-PA release (area under the BK curve) was ~25% lower (p&lt;0.05) in the adults with elevated (307±33 ng/100mL tissue) vs. normal (396±27 ng/100mL tissue) BP. Importantly, net endothelial release rate (from -1.5±1.0 to 40.6±4.3 ng/100mL tissue/min) and total amount of t-PA released (222±28 ng/100mL tissue) in response to BK were markedly lower (~25% and 30%, respectively, P&lt;0.05) in the elevated BP and short sleep duration group compared with the elevated BP and normal sleep duration group. In the elevated BP population, sleep duration was positively correlated with total t-PA release (r=0.46, P&lt;0.05). There was no effect of SNP on t-PA release in any group. In summary, insufficient sleep is associated with exacerbated impairments in t-PA release in adults with elevated BP.

Cardiometabolic effects of a novel SIRT1 activator, SRT2104, in people with type 2 diabetes mellitus

BackgroundThe cardiometabolic effects of SRT2104, a novel SIRT1 activator, were investigated in people with type 2 diabetes mellitus (T2DM).MethodsFifteen adults with T2DM underwent a randomised, double-blind, placebo-controlled cross-over trial and...

Lack of linear correlation between dynamic and steady-state cerebral autoregulation.

Key points For correct application and interpretation of cerebral autoregulation (CA) measurements in research and in clinical care, it is essential to understand differences and similarities between dynamic and steady‐state CA.The present study found no correlation between dynamic and steady‐state CA indices in healthy older adults.There was variability between individuals in all (steady‐state and dynamic) autoregulatory indices, ranging from low (almost absent) to highly efficient CA in this healthy population.These findings challenge the assumption that assessment of a single CA parameter or a single set of parameters can be generalized to overall CA functioning. Therefore, depending on specific research purposes, the choice for either steady‐state or dynamic measures or both should be weighed carefully. The present study aimed to investigate the relationship between dynamic (dCA) and steady‐state cerebral autoregulation (sCA). In 28 healthy older adults, sCA was quantified by a linear regression slope of proportionate (%) changes in cerebrovascular resistance (CVR) in response to proportionate (%) changes in mean blood pressure (BP) induced by stepwise sodium nitroprusside (SNP) and phenylephrine (PhE) infusion. Cerebral blood flow (CBF) was measured at the internal carotid artery (ICA) and vertebral artery (VA) and CBF velocity at the middle cerebral artery (MCA). With CVR = BP/CBF, Slope‐CVRICA, Slope‐CVRVA and Slope‐CVRiMCA were derived. dCA was assessed (i) in supine rest, analysed with transfer function analysis (gain and phase) and autoregulatory index (ARI) fit from spontaneous oscillations (ARIBaseline), and (ii) with transient changes in BP using a bolus injection of SNP (ARISNP) and PhE (ARIPhE). Comparison of sCA and dCA parameters (using Pearson's r for continuous and Spearman's ρ for ordinal parameters) demonstrated a lack of linear correlations between sCA and dCA measures. However, comparisons of parameters within dCA and within sCA were correlated. For sCA slope‐CVRVA with Slope‐CVRiMCA (r = 0.45, P < 0.03); for dCA ARISNP with ARIPhE (ρ = 0.50, P = 0.03), ARIBaseline (ρ = 0.57, P = 0.03) and PhaseLF (ρ = 0.48, P = 0.03); and for GainVLF with GainLF (r = 0.51, P = 0.01). By contrast to the commonly held assumption based on an earlier study, there were no linear correlations between sCA and dCA. As an additional observation, there was strong inter‐individual variability, both in dCA and sCA, in this healthy group of elderly, in a range from low to high CA efficiency.

CRF1 and CRF2 receptors in the bed nucleus of stria terminalis differently modulate the baroreflex function in unanesthetized rats.

The baroreflex is an important blood pressure regulating mechanism. The bed nucleus of stria terminalis (BNST) modulates the baroreflex function. However, the local BNST neurochemical mechanisms involved in control of baroreflex responses are not completely understood. Therefore, in this study, we investigated the involvement of corticotropin-releasing factor (CRF) receptors within the BNST in baroreflex control of heart rate in unanesthetized rats. For this, we evaluated effects of bilateral microinjection into the BNST of either the selective CRF1 receptor antagonist CP376395 (5nmol/100nL) or the selective CRF2 receptor antagonist antisauvagine-30 (5nmol/100nL) in bradycardiac response evoked by blood pressure increases caused by intravenous infusion of phenylephrine as well as tachycardiac response to blood pressure decrease caused by intravenous infusion of sodium nitroprusside. Bilateral microinjection of CP376395 into the BNST decreased the baroreflex bradycardiac response without affecting the reflex tachycardia. Conversely, BNST treatment with antisauvagine-30 decreased heart rate response during blood pressure drop without affecting the reflex bradycardia. Overall, these findings provide evidence of an involvement of CRF neurotransmission within the BNST in baroreflex activity. Nevertheless, data indicate that local CRF1 and CRF2 receptors differently modulate the baroreflex control of heart rate.

Chronic fluoxetine treatment enhances sympathetic activities associated with abnormality of baroreflex function in conscious normal rats

Data regarding the effects of selective serotonin reuptake inhibitors (SSRIs), which are a common type of antidepressants, on cardiovascular autonomic function are inconsistent. The present study was conducted to determine the effects of chronic fluoxetine, an SSRI, on blood pressure, cardiac autonomic nervous activities and baroreflex control of heart rate. Male Sprague-Dawley rats were treated with fluoxetine (10mg/kg day, p.o.) or saline for 14 weeks. Baroreflex function was determined by the sigmoid logistic method based on the heart rate responses to changes in blood pressure elicited by phenylephrine or sodium nitroprusside infusions. Cardiac sympathetic and parasympathetic tones were determined after methylatropine and propranolol treatments. Vascular responsiveness to acetylcholine, phenylephrine and sodium nitroprusside, and cardiac responsiveness to isoproterenol were determined after ganglionic blockade. Chronic fluoxetine treatment increased plasma levels of adrenaline and noradrenaline, but not nitric oxide. Elevation of blood pressure and heart rate by chronic fluoxetine was accompanied by baroreflex resetting and depressed baroreflex sensitivity. Elevated heart rate was mediated by enhanced sympathetic and depressed parasympathetic tones. The lowered baroreflex sensitivity might be attributed to attenuation of the parasympathetic component of baroreflex function. Chronic fluoxetine also diminished cardiac and vascular responsiveness to isoproterenol and acetylcholine, respectively. The plasma levels of adrenaline and noradrenaline were highly correlated with blood pressure, heart rate and baroreflex sensitivity. In conclusion, our results demonstrate that chronic fluoxetine treatment in normal rats induced predominant sympathoexcitation and depressed parasympathetic activity leading to mild hypertension, tachycardia, and impairment of baroreflex function.

Wavelet Analysis of Cardiac Baroreflex Sensitivity during Stepwise Blood Pressure Changes

BackgroundCardiac baroreflex regulates short‐term fluctuations in blood pressure (BP) via controlling heart rate (HR). The objective of this study was to determine the effect of steady‐state BP changes on cardiac baroreflex sensitivity (BRS) using wavelet analysis.MethodsThirteen subjects (67±7 years, 8 women) were tested during intravenous infusions of sodium nitroprusside (SNP) and phenylephrine (PE). Drug dosage was increased stepwise after achieving steady‐state BP in each stage. BRS was calculated from the beat‐by‐beat changes in systolic BP and RR interval within the frequency band of 0.02–0.20 Hz. Linear mixed model was used to analyze the effect of steady‐state BP changes on BRS.ResultsSNP infusion decreased mean arterial pressure (MAP) by 15% and increased HR by 12%. In contrast, PE infusion increased MAP by 23% and decreased HR by 3%. Representative wavelet map of BRS estimation during drug infusions is shown below. During SNP and PE infusions, there was a positive association between changes in steady‐state MAP and BRS (P&lt;0.001). Furthermore, the slope of BRS reduction with decreasing MAP during SNP infusion was greater than that during PE infusion (0.085±0.014 vs. 0.042±0.011 ms/mmHg per 1 mmHg change in MAP, P=0.004).ConclusionsSteady‐state decrease in BP is associated with elevation of HR and marked reduction of BRS. These findings suggest that dynamic short‐term regulation of BP during hypotension may be impaired and elevate the risk of fall or syncope.Support or Funding InformationThis study was supported by the NIH (R01AG033106 and K99HL133449) and the Americann Heart Association (14POST20140013).

Increased NO Sensitivity is Associated with Maintained Coronary Microvascular cGMP‐PDE5 Signaling in Exercising Swine with Multiple Co‐Morbidities

BackgroundMultiple comorbidities, including diabetes mellitus (DM), hypercholesterolemia (HC) and chronic kidney disease (CKD) are thought to cause coronary microvascular dysfunction through a reduction in microvascular NO signaling, leading to impaired myocardial perfusion. Here we investigated whether NO‐cGMP‐PDE5 coronary microvascular signaling is modified in swine with DM+HC+CKD, by studying the vasodilator responses to PDE5 inhibition and to exogenous NO in chronically instrumented swine.Methods and resultsFive female swine (DM+HC+CKD) with Diabetes Mellitus (streptozotocin 3×50mg/kg), chronic kidney disease (renal embolization) were fed high fat diet for 6 months, while six healthy female swine served as controls (CON). Hyperglycemia (21±1.4 vs 8.9±1.5mmol/l in in DM+HC+CKD vs CON, P=0.0002), hypercholesterolemia (7.8±1.0 vs 2.8±1.2mmol/l, P=0.013) and chronic kidney disease (GFR: 123±12 vs 191±9ml/min, P=0.001) were present. Myocardial oxygen delivery was impaired in DM+HC+CKD swine, forcing the myocardium to increase its oxygen extraction both at rest and during exercise (Figure), and resulting in reduced coronary venous oxygen content compared to CON (both P&lt;0.05). PDE5 inhibition with sildenafil (8mg i.v.) decreased myocardial oxygen extraction in both DM+HC+CKD (P=0.016) and CON (P=0.005, Figure), to a similar extent (P=0.34), indicating maintained NO‐cGMP vasodilator influence. As myocardial NO production was decreased (0.19±0.03 vs 0.34±0.13μM NO2−+NO3−/mg protein, P=0.02), we investigated whether an increase in NO sensitivity contributed to maintain NO‐cGMP vasodilator influence, by infusion of the NO donor sodium nitroprusside (SNP). Coronary vascular conductance (CVC) decreased more in DM+HC+CKD compared to CON, indicating an increased NO‐sensitivity (P=0.043, Figure).ConclusionIn swine with multiple co‐morbidities reduced bioavailability of NO appears to be compensated by increased sensitivity to NO, which is associated with maintained cGMP‐mediated vasodilator influence.Support or Funding InformationFunding: This study was supported by grants from the European Commission FP7‐Health‐2010 grant MEDIA‐261409, the Netherlands CardioVascular Research Initiative: an initiative with support of the Dutch Heart Foundation [CVON2014‐11 (RECONNECT)].

Effect of nitric oxide on renal autoregulation during hypothermia in the rat

Hypothermia-induced reduction of metabolic rate is accompanied by depression of both glomerular perfusion and filtration. The present study investigated whether these changes are linked to changes in renal autoregulation and nitric oxide (NO) signalling. During hypothermia, renal blood flow (RBF) and glomerular filtration rate (GFR) were reduced and urine production was increased, and this was linked with reduced plasma cGMP levels and increased renal vascular resistance. Although stimulation of NO production decreased vascular resistance, blood pressure and urine flow, intravenous infusion of the NO precursor L-arginine or the NO donor sodium nitroprusside did not alter RBF or GFR. In contrast, inhibition of NO synthesis by Nw-nitro-L-arginine led to a further decline in both parameters. Functional renal autoregulation was apparent at both temperatures. Below the autoregulatory range, RBF in both cases increased in proportion to the perfusion ±pressure, although, the slope of the first ascending limb of the pressure-flow relationship was lower during hypothermia. The main difference was rather that the curves obtained during hypothermia levelled off already at a RBF of 3.9 ± 0.3 mL/min then remained stable throughout the autoregulatory pressure range, compared to 7.6 ± 0.3 mL/min during normothermia. This was found to be due to a threefold increase in, primarily, the afferent arteriolar resistance from 2.6 to 7.5 mmHg min mL−1. Infusion of sodium nitroprusside did not significantly affect RBF during hypothermia, although a small increase at pressures below the autoregulatory range was observed. In conclusion, cold-induced rise in renal vascular resistance results from afferent arteriolar vasoconstriction by the autoregulatory mechanism, setting RBF and GFR in proportion to the metabolic rate, which cannot be explained by reduced NO production alone.

Mean arterial pressure‐embedded model for real‐time simulation and controller validation

The lack of models for automatic control of mean arterial pressure (MAP), in real-time, associated with variability in response to sodium nitroprusside infusion, makes it impossible to validate automatic MAP controllers. Therefore, this Letter presents a low-cost innovative real-time model to MAP. Therefore, the authors used a variation of the mathematical model of Slate, implemented in MATLAB®. The system was developed with the capabilities of Simulink® and deployed to a single-board computer. The results showed that the embedded model presented an error <3% for a target MAP of 100 mmHg, allowing the use of this model, in real time, for validation of embedded MAP controllers.

Effect of hypohydration on postsynaptic cutaneous vasodilation and sweating in healthy men.

Hypohydration decreases cutaneous vasodilation and sweating during heat stress, but it is unknown if these decrements are from postsynaptic (i.e., sweat gland/blood vessel) alterations. The purpose of this study was to determine if hypohydration affects postsynaptic cutaneous vasodilation and sweating responses. Twelve healthy men participated in euhydrated (EU) and hypohydrated (HY) trials, with hypohydration induced via fluid restriction and passive heat stress. Changes in cutaneous vascular conductance (CVC; %max) in response to incremental intradermal infusion of the endothelium-independent vasodilator sodium nitroprusside (SNP) and the endothelium-dependent vasodilator methacholine chloride (MCh) were assessed by laser Doppler flowmetry. Local sweat rate (LSR) was simultaneously assessed at the MCh site via ventilated capsule. At the end of the last dose, maximal CVC was elicited by delivering a maximal dose of SNP (5 × 10-2 M) for 30 min to both sites with simultaneous local heating (~44°C) at the SNP site. The concentration of drug needed to elicit 50% of the maximal response (log EC50) was compared between hydration conditions. The percent body mass loss was greater with HY vs. EU (-2.2 ± 0.7 vs. -0.1 ± 0.7%, P < 0.001). Log EC50 of endothelium-dependent CVC was lower with EU (-3.62 ± 0.22) vs. HY (-2.93 ± 0.08; P = 0.044). Hypohydration did not significantly alter endothelium-independent CVC or LSR (both P > 0.05). In conclusion, hypohydration attenuated endothelium-dependent CVC but did not affect endothelium-independent CVC or LSR responses. These data suggest that reductions in skin blood flow accompanying hypohydration can be partially attributed to altered postsynaptic function.

Uric acid and endothelial function in elderly community-dwelling subjects

The role of serum uric acid (SUA), an inflammatory agent and potential mediator of cardiovascular diseases, in endothelial function (EF) has been tested only in middle-aged subjects affected by specific diseases. Our aim was to assess the relationship between SUA and measures of EF in a cohort of elderly community-dwellers. This study involved 424 males and 426 females aged 70years from the Prospective Study of the Vasculature in Uppsala Seniors (PIVUS), having complete data on SUA and EF assessed by flow-mediated vasodilation (FMD) and by intra-arterial infusion of acetylcholine (endothelium-dependent vasodilation, EDV) and sodium nitroprusside (endothelium-independent vasodilation, EIDV). Univariate and multivariate regression models obtained by backward selection from initial fully-adjusted models were built to assess the relationship between SUA and measures of EF in both genders. Cardiovascular risk factors, serum hormonal and metabolic mediators, and body composition were considered as potential confounders. In the univariate model, SUA was inversely associated in both genders with log(EDV) (β±SE males −0.39±0.17, p=0.03; females −0.57±0.19, p=0.003) and log(EIDV) (males −0.23±0.12, p=0.05; females −0.49±0.15, p=0.002), but not with log(FMD). After adjustment for BMI, only the association between SUA and log(EIDV) in females persisted, though attenuated (−0.32±0.16, p=0.049), and was no longer significant in the fully-adjusted multivariate model including waist/hip ratio. In conclusion, in older subjects, especially women, SUA is associated with EF not independently of a list of confounders including BMI and trunk fat mass, suggesting a role as surrogate metabolic marker rather than an active player in EF.

Taurine Supplementation Reduces Renal Nerve Activity in Male Rats in which Renal Nerve Activity was Increased by a High Sugar Diet.

This study tests the hypothesis that taurine supplementation reduces sugar-induced increases in renal sympathetic nerve activity related to renin release in adult male rats. After weaning, male rats were fed normal rat chow and drank water containing 5% glucose (CG) or water alone (CW) throughout the experiment. At 6-7 weeks of age, each group was supplemented with or without 3% taurine in drinking water until the end of experiment. At 7-8 weeks of age, blood chemistry and renal nerve activity were measured in anesthetized rats. Body weights slightly and significantly increased in CG compared to CW groups but were not significantly affected by taurine supplementation. Plasma electrolytes except bicarbonate, plasma creatinine, and blood urea nitrogen were not significantly different among the four groups. Mean arterial pressure significantly increased in both taurine treated groups compared to CW, while heart rates were not significantly different among the four groups. Further, all groups displayed similar renal nerve firing frequencies at rest and renal nerve responses to sodium nitroprusside and phenylephrine infusion. However, compared to CW group, CG significantly increased the power density of renin release-related frequency component, decreased that of sodium excretion-related frequency component, and decreased that of renal blood flow-related frequency component. Taurine supplementation completely abolished the effect of high sugar intake on renal sympathetic activity patterns. These data indicate that in adult male rats, high sugar intake alters the pattern but not firing frequency of sympathetic nerve activity to control renal function, and this effect can be improved by taurine supplementation.

Effect of intracoronary nitroprusside injection on flow recovery during primary PCI in acute STEMI patients.

The no/slow reflow phenomenon during primary percutaneous coronary intervention (PPCI) causes the destruction of the coronary microcirculation and further myocardial damage. Some studies have shown that intracoronary nitroprusside infusion is a safe and effective method for managing the no/slow reflow phenomenon. However, it is uncertain whether the injection of nitroprusside at a specific time point during PPCI can most effectively prevent no-reflow. In this study, we investigated the effect of the timing of an intracoronary nitroprusside injection on flow recovery during PPCI in patients with ST elevation acute myocardial infarction (STEMI). One hundred twenty consecutive patients with STEMI who underwent PPCI were enrolled in the study. Patients who fulfilled the eligibility criteria were randomly allocated to three groups: control group (N.=40) received no nitroprusside before they completed PCI; the second group (N.=40) received nitroprusside before balloon dilatation; and the third group (N.=40) received nitroprusside after each balloon dilatation and before contrast agent refilling. The baseline clinical variables and the details of the PCI procedure were collected. The thrombolysis in myocardial infarction (TIMI) flow grades and the corrected TIMI frame count (cTFC) were evaluated immediately after stent implantation was completed. There were no significant differences in the baseline characteristics, antithrombotic drugs given before PCI, and details of the PCI procedure among the three groups (P>0.05). The incidence of TIMI grade 3 after PCI was significantly higher in the nitroprusside group than in the control group (P=0.025), whereas cTFC was significantly lower in the nitroprusside group (26.6±15.2) than in the control group (38.1±21.3, P=0.001). The incidence of TIMI grade 3 after PCI was significantly higher in the third group than in the second group (P=0.045), and cTFC was significantly lower in the third group (21.5±9.5) than in the second group (31.2±18.3, P=0.002). Multivariable linear regression analyses showed that the intracoronary nitroprusside injection time was a significant predictor of cTFC after PCI. These data suggest that the intracoronary injection of nitroprusside significantly reduced the incidence of no/slow reflow during PPCI. The intracoronary injection of nitroprusside most effectively prevented the no/slow reflow phenomenon when administered between balloon dilatation and contrast agent refilling during PPCI.

Comparison in Conscious Rabbits of the Baroreceptor-Heart Rate Reflex Effects of Chronic Treatment with Rilmenidine, Moxonidine, and Clonidine.

We investigated the effects of chronic subcutaneous treatment with centrally-acting antihypertensive agents moxonidine, rilmenidine, and clonidine on the baroreflex control of heart rate (HR) in conscious normotensive rabbits over 3 weeks. Infusions of phenylephrine and nitroprusside were performed at week 0 and at weeks 1 and 3 of treatment to determine mean arterial pressure (MAP)-HR baroreflex relationships. A second curve was performed after intravenous methscopolamine to determine the sympathetic baroreflex relationship. The vagal component of the reflex was determined by subtracting the sympathetic curve from the intact curve. Clonidine and moxonidine (both 1 mg/kg/day), and rilmenidine (5 mg/kg/day), reduced MAP by 13 ± 3, 15 ± 2, and 13 ± 2 mmHg, respectively, but had no effect on HR over the 3-week treatment period. Whilst all three antihypertensive agents shifted baroreflex curves to the left, parallel to the degree of hypotension, moxonidine and rilmenidine decreased the vagal contribution to the baroreflex by decreasing the HR range of the reflex but moxonidine also increased sympathetic baroreflex range and sensitivity. By contrast clonidine had little chronic effect on the cardiac baroreflex. The present study shows that second generation agents moxonidine and rilmenidine but not first generation agent clonidine chronically shift the balance of baroreflex control of HR toward greater sympathetic and lesser vagal influences. These changes if translated to hypertensive subjects, may not be particularly helpful in view of the already reduced vagal contribution in hypertension.