Sympatho-renal interactions in the determination of arterial pressure: role in hypertension

Applications of the ultrasound-guided nerve block technique for nonanalgesic effects

The nerve block technique guided by ultrasound has been able to accurately block tiny nerves throughout the body in recent years. It has been increasingly used to treat multisystem diseases or analgesia in surgical patients, but the latter accounted for the vast majority of cases. The nonanalgesic effect of nerve blocks is also in wide demand. After searching ultrasound-guided nerve block works on the PubMed database, we systematically summarized the current clinical application of the nerve block technique and the unique role and related mechanism of nerve block in the prevention and treatment of multi-system diseases or symptoms, including disorders of the circulatory and respiratory systems, postoperative cognitive dysfunction, immune function, posttraumatic stress disorder, and postoperative digestive system, to put forward the potential prospective application in future and serve as a reference for future research of nerve block therapy in these diseases mentioned.

Bidirectional asymmetry in the neurovisceral communication for the cardiovascular control: New insights

The cardiovascular control involves a bidirectional functional connection between the brain and heart. We hypothesize that this connection could be extended to other organs using endocrine and autonomic nervous systems (ANS) as communication pathways. This implies a neuroendocrine interaction controlling particularly the cardiovascular function where the enzymatic cascade of the renin-angiotensin system (RAS) plays an essential role. It acts not only through its classic endocrine connection but also the ANS. In addition, the brain is functionally, anatomically, and neurochemically asymmetric. Moreover, this asymmetry goes even beyond the brain and it includes both sides of the peripheral nervous and neuroendocrine systems. We revised the available information and analyze the asymmetrical neuroendocrine bidirectional interaction for the cardiovascular control. Negative and positive correlations involving the RAS have been observed between brain, heart, kidney, gut, and plasma in physiologic and pathologic conditions. The central role of the peptides and enzymes of the RAS within this neurovisceral communication, as well as the importance of the asymmetrical distribution of the various RAS components in the pathologies involving this connection, are particularly discussed. In conclusion, there are numerous evidences supporting the existence of a neurovisceral connection with multiorgan involvement that controls, among others, the cardiovascular function. This connection is asymmetrically organized.

Endogenous hydrogen peroxide in paraventricular nucleus mediates sympathetic activation and enhanced cardiac sympathetic afferent reflex in renovascular hypertensive rats

An enhancement of the cardiac sympathetic afferent reflex (CSAR) contributes to sympathetic activation in renovascular hypertension. Angiotensin II in the paraventricular nucleus (PVN) augments the CSAR and increases sympathetic outflow and blood pressure. The present study aimed to determine whether endogenous hydrogen peroxide in the PVN mediated the enhanced CSAR, sympathetic activity and the effects of angiotensin II in the PVN in renovascular hypertension induced by the two-kidney, one-clip method (2K1C) in rats. At the end of the fourth week, the rats underwent sino-aortic and vagal denervation under general anaesthesia with urethane and α-chloralose. Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded. The CSAR was evaluated by the RSNA response to epicardial application of bradykinin. Microinjection of polyethylene glycol-catalase (PEG-CAT), an analogue of endogenous catalase, into the PVN decreased the RSNA and MAP and abolished the CSAR in both sham-operated and 2K1C rats. Microinjection into the PVN of the catalase inhibitor, aminotriazole, increased the RSNA and MAP and enhanced the CSAR. The effects of PEG-CAT or aminotriazole were greater in 2K1C rats than in sham-operated animals. The effects of angiotensin II in the PVN were abolished by pretreatment with PEG-CAT in both sham-operated and 2K1C rats; however, aminotriazole failed to potentiate the effects of angiotensin II. The catalase activity was decreased but the H(2)O(2) levels were increased in the PVN of 2K1C rats. These results indicate that endogenous H(2)O(2) in the PVN not only mediates the enhanced sympathetic activity and CSAR, but also the effects of angiotensin II in the PVN in renovascular hypertensive rats.

Superoxide anions in the paraventricular nucleus mediate the enhanced cardiac sympathetic afferent reflex and sympathetic activity in renovascular hypertensive rats

An enhanced cardiac sympathetic afferent reflex (CSAR) is involved in the sympathetic activation in renovascular hypertension. The present study was designed to determine the role of superoxide anions in the paraventricular nucleus (PVN) in mediating the enhanced CSAR and sympathetic activity in renovascular hypertension in the two-kidney, one-clip (2K1C) model. Sinoaortic denervation and vagotomy were carried out, and renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were recorded under anesthesia. The CSAR was evaluated by the response of RSNA to the epicardial application of capsaicin. Superoxide anion levels and NAD(P)H oxidase activity in the PVN increased in 2K1C rats and were much higher in 2K1C rats than in sham-operated (sham) rats after the epicardial application of capsaicin or PVN microinjection of ANG II. In both 2K1C and sham rats, PVN microinjection of the superoxide anion scavenger tempol or the NAD(P)H oxidase inhibitor apocynin abolished the CSAR, whereas the SOD inhibitor diethyldithiocarbamic acid (DETC) potentiated the CSAR. Tempol and apocynin decreased but DETC increased baseline RSNA and MAP. ANG II in the PVN caused larger responses of the CSAR, baseline RSNA, and baseline MAP in 2K1C rats than in sham rats. The effects of ANG II were abolished by pretreatment with tempol or apocynin in both 2K1C and sham rats and augmented by DETC in the PVN in 2K1C rats. These results indicate that superoxide anions in the PVN mediate the CSAR and the effects of ANG II in the PVN. Increased superoxide anions in the PVN contribute to the enhanced CSAR and sympathetic activity in renovascular hypertension.

Intermittent hypoxia: cause of or therapy for systemic hypertension?

During acute episodes of hypoxia, chemoreceptor-mediated sympathetic activity increases heart rate, cardiac output, peripheral resistance and systemic arterial pressure. However, different intermittent hypoxia paradigms produce remarkably divergent effects on systemic arterial pressure in the post-hypoxic steady state. The hypertensive effects of obstructive sleep apnea (OSA) vs. the depressor effects of therapeutic hypoxia exemplify this divergence. OSA, a condition afflicting 15-25% of American men and 5-10% of women, has been implicated in the pathogenesis of systemic hypertension and is a major risk factor for heart disease and stroke. OSA imposes a series of brief, intense episodes of hypoxia and hypercapnia, leading to persistent, maladaptive chemoreflex-mediated activation of the sympathetic nervous system which culminates in hypertension. Conversely, extensive evidence in animals and humans has shown controlled intermittent hypoxia conditioning programs to be safe, efficacious modalities for prevention and treatment of hypertension. This article reviews the pertinent literature in an attempt to reconcile the divergent effects of intermittent hypoxia therapy and obstructive sleep apnea on hypertension. Special emphasis is placed on research conducted in the nations of the former Soviet Union, where intermittent hypoxia conditioning programs are being applied therapeutically to treat hypertension in patients. Also reviewed is evidence regarding mechanisms of the pro- and anti-hypertensive effects of intermittent hypoxia.

Elevated renal norepinephrine in proANP gene-disrupted mice is associated with increased tyrosine hydroxylase expression in sympathetic ganglia

The sympatholytic properties of atrial natriuretic peptide (ANP) contribute to its vasodilatory and natriuretic effects. High circulating catecholamine levels, along with renal dysfunction, present in proANP gene-disrupted (-/-) mice are thought to contribute to the hypertension characteristic of this model. To further understand the mechanism by which the absence of ANP leads to stimulation of sympathetic activity we measured tyrosine hydroxylase expression in mice with and without ANP. The adrenal and prevertebral ganglionic expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine production, was significantly increased in ANP -/- mice. ANP's sympatholytic properties include the depression of ganglionic and adrenal TH expression and catecholamine production. Thus, these results suggest that the absence of ANP's sympatholytic effects is not completely compensated for in ANP -/- mice. In addition, mice devoid of ANP display an increase in renal sympathetic nerve activity from birth through to adulthood which may lead to structural and/or functional changes in the early postnatal kidney that contribute to the hypertensive phenotype of ANP -/- mice. The over-activation of the sympathetic nervous system in mice lacking ANP confirms the important role of this peptide in the modulation of sympathetic nerve activity and its contribution to blood pressure homeostasis.

Intravenous insulin-like growth factor-I receptor antisense treatment reduces angiotensin receptor expression and function in spontaneously hypertensive rats

The present study investigated the effects of a functional deficit in insulin-like growth factor-I signaling via chronic intravenous administration of insulin-like growth factor-I (IGF-I) receptor antisense in the conscious spontaneously hypertensive rat cardiovascular system. Insulin-like growth factor-I receptor (IGF-IR) antisense, but not full mismatch treatment, decreased IGF-IR expression in both conductance and resistance blood vessels. Aortic IGF-IR density was reduced by 67.4 +/- 6.0% in antisense-treated spontaneously hypertensive rat (SHR) compared with untreated animals, whereas mismatch treatment had no effect (analysis of variance, n = 3, P < 0.01). Aortic and tail artery angiotensin II type 1 receptor expression was significantly reduced by IGF-IR antisense treatment, whereas angiotensin II type 2 receptor expression was unaffected by administration of antisense and mismatch oligonucleotides. IGF-I receptor antisense treatment caused a significant decrease in pressor responses to angiotensin II in comparison with full-length mismatch treatment (E(max) was reduced to 65 +/- 7 mm Hg compared with 99 +/- 6 mm Hg, p < 0.05). Likewise, a reduction in pressor responses to noradrenaline was observed in hypertensive rats treated with IGF-IR antisense compared with full mismatch-treated rats (E(max) was reduced to 60 +/- 6 mm Hg compared with 108 +/- 5 mm Hg, p < 0.01). There was no clear antisense effect on resting blood pressure and no effect at on aortic medial thickness. These results suggest that although the proliferative and vasodilator effects of IGF-I are impaired in SHR, the effects on angiotensin receptor expression remain profound.