Neuropeptide Y and sympathetic control of vascular tone in hypertension

Wavelet analysis of laser Doppler microcirculatory signals: Current applications and limitations

Laser Doppler flowmetry (LDF) has long been considered a gold standard for non-invasive assessment of skin microvascular function. Due to the laser Doppler (LD) microcirculatory signal's complex biological and physiological context, using spectral analysis is advisable to extract as many of the signal's properties as feasible. Spectral analysis can be performed using either a classical Fourier transform (FT) technique, which has the disadvantage of not being able to localize a signal in time, or wavelet analysis (WA), which provides both the time and frequency localization of the inspected signal. So far, WA of LD microcirculatory signals has revealed five characteristic frequency intervals, ranging from 0.005 to 2 Hz, each of which being related to a specific physiological influence modulating skin microcirculatory response, providing for a more thorough analysis of the signals measured in healthy and diseased individuals. Even though WA is a valuable tool for analyzing and evaluating LDF-measured microcirculatory signals, limitations remain, resulting in a lack of analytical standardization. As a more accurate assessment of human skin microcirculation may better enhance the prognosis of diseases marked by microvascular dysfunction, searching for improvements to the WA method is crucial from the clinical point of view. Accordingly, we have summarized and discussed WA application and its limitations when evaluating LD microcirculatory signals, and presented insight into possible future improvements. We adopted a novel strategy when presenting the findings of recent studies using WA by focusing on frequency intervals to contrast the findings of the various studies undertaken thus far and highlight their disparities.

Neuropeptide Y mediates cardiac hypertrophy through microRNA-216b/FoxO4 signaling pathway

Cardiac hypertrophy (CH) is a major risk factor for heart failure accompanied by maladaptive cardiac remodeling. The role and potential mechanism of neuropeptide Y (NPY) in CH are still unclear. We will explore the role and the mechanism of NPY inactivation (NPY-I) in CH caused by pressure overload. Abdominal aortic constriction (AAC) was used to induce CH model in rats. NPY or angiotensin II (Ang II) was used to trigger CH model in vitro in neonatal rat ventricular myocytes (NRVMs). We found that NPY was increased in the heart and plasma of hypertrophic rats. However, Ang II did not increase NPY expression in cardiomyocytes. NPY-I attenuated CH as decreasing CH-related markers (ANP, BNP and β-MHC mRNA) level, reducing cell surface area, and restoring cardiac function. NPY inactivation increased miR-216b and decreased FoxO4 expression in CH heart. Moreover, NPY decreased miR-216b and increased FoxO4 expression in NRVMs which were reversed by NPY type 1 receptor (NPY1R) antagonist BIBO3304. MiR-216b mimic and FoxO4 siRNA (small interfering RNA) inhibited NPY/Ang II-induced myocardial hypertrophy in vitro. Meanwhile, BIBO3304 reversed the pro-hypertrophy effect of NPY in vitro. Collectively, NPY deficiency attenuated CH by NPY1R-miR-216b-FoxO4 axis. These findings suggested that NPY would be a potential therapeutic target for the prevention and treatment of cardiac hypertrophy.

Effects of high-fat diet on sympathetic neurotransmission in mesenteric arteries from Dahl salt-sensitive rat

Obesity hypertension is driven by sympathetic neurotransmission to the heart and blood vessels. We tested the hypothesis that high-fat diet (HFD)-induced hypertension is driven by sympathetic neurotransmission to mesenteric arteries (MA) in male but not female Dahl salt-sensitive (Dahl ss) rat. Rats were fed a control diet (CD; 10 kcal% from fat) or HFD (60 kcal% from fat) beginning at 3 weeks (wk) of age; measurements were made at 10-, 17- and 24-wk. Body weight increased with HFD, age and sex. Mean arterial pressure (MAP) was higher in HFD versus CD rats from both sexes at 17- and 24-wk. MA constriction measured using pressure myography, and electrical field stimulation (EFS, 0.2-30 Hz) was greater in HFD versus CD in males at 17-wk; this was not due to changes in α2 autoreceptor or norepinephrine transporter (NET) function. Prazosin (α1-AR antagonist) and suramin (P2 receptor antagonist) inhibited neurogenic MA constriction equally in all groups. Arterial reactivity to exogenous norepinephrine (NE; 10^-8 - 10^-5 M) was lower in HFD versus CD at 10-wk in males. Female MA reactivity to exogenous ATP was lower at 24-weeks compared to earlier time points. HFD did not affect tyrosine hydroxylase (TH) or the vesicular nucleotide transporter (VNUT) nerve density in MA from both sexes. NE content was lower in MA but higher in plasma at 24-wk compared to 10- and 17-wk in both sexes. In conclusion, HFD-induced hypertension is not driven by increased sympathetic neurotransmission to MA in male and female Dahl ss rats.

Peripheral cardiac sympathetic hyperactivity in cardiovascular disease: role of neuropeptides

High levels of sympathetic drive in several cardiovascular diseases including postmyocardial infarction, chronic congestive heart failure and hypertension are reinforced through dysregulation of afferent input and central integration of autonomic balance. However, recent evidence suggests that a significant component of sympathetic hyperactivity may also reside peripherally at the level of the postganglionic neuron. This has been studied in depth using the spontaneously hypertensive rat, an animal model of genetic essential hypertension, where larger neuronal calcium transients, increased release and impaired reuptake of norepinephrine in neurons of the stellate ganglia lead to a significant tachycardia even before hypertension has developed. The release of additional sympathetic cotransmitters during high levels of sympathetic drive can also have deleterious consequences for peripheral cardiac parasympathetic neurotransmission even in the presence of β-adrenergic blockade. Stimulation of the cardiac vagus reduces heart rate, lowers myocardial oxygen demand, improves coronary blood flow, and independently raises ventricular fibrillation threshold. Recent data demonstrates a direct action of the sympathetic cotransmitters neuropeptide Y (NPY) and galanin on the ability of the vagus to release acetylcholine and control heart rate. Moreover, there is as a strong correlation between plasma NPY levels and coronary microvascular function in patients with ST-elevation myocardial infarction being treated with primary percutaneous coronary intervention. Antagonists of the NPY receptors Y1 and Y2 may be therapeutically beneficial both acutely during myocardial infarction and also during chronic heart failure and hypertension. Such medications would be expected to act synergistically with β-blockers and implantable vagus nerve stimulators to improve patient outcome.

Enhanced neuropeptide Y synthesis during intermittent hypoxia in the rat adrenal medulla: role of reactive oxygen species-dependent alterations in precursor peptide processing

Intermittent hypoxia (IH) associated with recurrent apneas often leads to cardiovascular abnormalities. Previously, we showed that IH treatment elevates blood pressure and increases plasma catecholamines (CAs) in rats via reactive oxygen species (ROS)-dependent enhanced synthesis and secretion from the adrenal medulla (AM). Neuropeptide Y (NPY), a sympathetic neurotransmitter that colocalizes with CA in the AM, has been implicated in blood pressure regulation during persistent stress. Here, we investigated whether IH facilitates NPY synthesis in the rat AM and assessed the role of ROS signaling. IH increased NPY-like immunoreactivity in many dopamine-β-hydroxylase-expressing chromaffin cells with a parallel increase in preproNPY mRNA and protein. IH increased the activities of proNPY-processing enzymes, which were due, in part, to elevated protein expression and increased proteolytic processing. IH increased ROS generation, and antioxidants reversed IH-induced increases in ROS, preproNPY, and its processing to bioactive NPY in the AM. IH treatment increased blood pressure and antioxidants and inhibition of NPY amidation prevented this response. These findings suggest that IH-induced elevation in NPY expression in the rat AM is mediated by ROS-dependent augmentation of preproNPY mRNA expression and proNPY-processing enzyme activities and contributes to IH-induced elevation of blood pressure.

Prenatal stress in the rat results in increased blood pressure responsiveness to stress and enhanced arterial reactivity to neuropeptide Y in adulthood

We have shown previously that stress in the pregnant rat leads to a heightened cardiovascular response to restraint in adult offspring. The present study was undertaken to explore further the persistent cardiovascular effects of prenatal stress, with a focus on peripheral vascular function. Sprague-Dawley female rats were exposed to restraint/bright light three times daily in the last week of pregnancy. Litters from stressed and control females were cross-fostered to control dams to eliminate possible effects of maternal stress on nursing behaviour. At 120 days, offspring cardiovascular variables were measured by radiotelemetry. Reactivity of mesenteric small arteries was assessed by myography, and responses to electrical field stimulation determined. Resting cardiovascular parameters in prenatally stressed (PS) offspring were similar to controls but PS rats showed a greater increase in systolic blood pressure following restraint stress (P<0.05). Recovery was also prolonged in PS animals compared with controls and was of longer duration in PS females than in PS males (P<0.05). Adult PS females, but not males, also had elevated basal plasma corticosterone levels in comparison with controls (P<0.05). Vascular reactivity to neuropeptide Y (P<0.05) and electrical field stimulation (P<0.05) in mesenteric arteries was also significantly increased in PS animals. Vascular responses to adrenergic agonists as well as endothelial dilator function did not differ between PS and controls. We conclude that prenatal stress during late gestation has long-lasting effects on cardiovascular responsiveness and vascular reactivity to neuropeptide Y in the offspring.