Myogenic Reaction Research Articles

Mechanisms of neurovascular coupling

The brain is characterized by a well-developed vascular network and consumes a significant proportion of cardiac output relative to its mass. Normally, the metabolic needs of the brain significantly depend on the intensity of the functioning of its various departments, which requires constant regulation of the level of local blood flow. On the other hand, the state of systemic hemodynamics can have a significant impact on organ blood flow. Moreover, the importance of accurate and prompt regulation of cerebral blood flow is determined by the lack of energy reserves or substrates for its autonomous production in the nervous tissue and the huge role of the central nervous system in ensuring all physiological processes. In this regard, the organ cerebral blood flow has complex physiological mechanisms of regulation, which are implemented at various levels. At the same time, myogenic reactions are isolated, which occur when the degree of stretching of the smooth muscle cells of the vascular wall changes under the influence of pressure in the lumen of the vessel, as well as under the influence of local humoral effects, including those exerted by metabolites, on vascular tone at the level of the neurovascular unit. This review considers in detail the role of the neurovascular unit in the regulation of cerebral blood flow and the provision of the so-called neurovascular conjugation – a flexible dynamic correspondence between the level of local neuronal activity and the delivery of oxygen and nutrients. The mechanisms and essential importance of neurovascular coupling in the regulation of local cerebral blood flow, which ensures the development of functional hyperemia, as well as the performance several other functions, such as the delivery and removal of metabolites, temperature regulation, and the formation of cerebrospinal fluid, are demonstrated.

Loss of TRPV2-mediated blood flow autoregulation recapitulates diabetic retinopathy in rats.

Loss of retinal blood flow autoregulation is an early feature of diabetes that precedes the development of clinically recognizable diabetic retinopathy (DR). Retinal blood flow autoregulation is mediated by the myogenic response of the retinal arterial vessels, a process that is initiated by the stretch‑dependent activation of TRPV2 channels on the retinal vascular smooth muscle cells (VSMCs). Here, we show that the impaired myogenic reaction of retinal arterioles from diabetic animals is associated with a complete loss of stretch‑dependent TRPV2 current activity on the retinal VSMCs. This effect could be attributed, in part, to TRPV2 channel downregulation, a phenomenon that was also evident in human retinal VSMCs from diabetic donors. We also demonstrate that TRPV2 heterozygous rats, a nondiabetic model of impaired myogenic reactivity and blood flow autoregulation in the retina, develop a range of microvascular, glial, and neuronal lesions resembling those observed in DR, including neovascular complexes. No overt kidney pathology was observed in these animals. Our data suggest that TRPV2 dysfunction underlies the loss of retinal blood flow autoregulation in diabetes and provide strong support for the hypothesis that autoregulatory deficits are involved in the pathogenesis of DR.

Irreversible brain death-Part 2. Spinalization phenomena

Spinal automatisms and reflexes, peripheral neurogenic and myogenic reactions are common in patients with irreversible brain death. They are therefore compatible and are even understood by experienced investigators as confirmation of irreversible brain death. This article provides an overview of the phenomenology of irreversible brain death and discusses it from a neuropathological perspective. Furthermore, irreversible brain death is described in order to distinguish it from pathological movements and motor reactions in comatose patients or patients with disturbed consciousness due to severe brain disorders.

ВОЗРАСТНЫЕ ОСОБЕННОСТИ РЕОЭНЦЕФАЛОГРАФИИ, СВЯЗАННЫЕ С ФАЗАМИ ДЫХАНИЯ

The article presents the results of a study on the cerebral hemodynamics of residents of the Volgograd region (165 respondents: 18–35 years old; 50–55 years; 56–60 years and over 61 years), making it possible to identify the parameters that are the most informative for assessing of blood supply disorders of the brain. Objective: to study the age features of cerebral blood circulation connected with breath phases. Evaluation of the functional state of the cerebral hemodynamics was carried out on the basis of comprehensive studies of blood supply to the brain (rest and against the background of respiratory test) using the method of reoencephalography. The reoencephalographic examination was performed in 4 leads (FM, OM left hemisphere; FM, OM right hemisphere). Indicators were registered: integral index of pulse filling, amplitude-frequency index, rheographic index, time of propagation of the rheographic wave, average vessel filling rate, venous outflow, dicrotic index, diastolic index. Decrease in total pulse blood filling of the brain at respondents of 50–55 years is revealed. In the dynamics of respiratory test myogenic reactions of vasoconstriction of resistive arteries of the brain in people of older age (50–55 years and older) are slightly expressed. The limit of vasoconstrictor reactions caused by the aging of the body is the cause of deterioration of the conditions of regional blood outflow. The inconsistency of the ratio of regional blood flow to its outflow is a marker of the reduction of adaptive reactions of the circulatory system of people over 50 years of age with an increase in venous pressure in the upper vena cava system. The information value, efficiency and safety of the reographic study at rest and against the background of respiratory test allows it to be recommended for inclusion in the plan of dispensary observations, especially those over 50 years of age.

The Lamé Problem Applied to a Blood Vessel with an Active Wall

Abstract—In this paper we consider a two-dimensional problem of the stress distribution in the wall of a blood vessel with a lumen size that may vary depending on activation of smooth-muscle cells. Based on experimental data, the dependence of the circumferential stress on the parameter of smooth-muscle activation was obtained and the dependence of the latter on the cell membrane potential was described. It has been shown that contractile activity in smooth muscles (myogenic reaction) produces a significant decrease in the stresses. The maximum value of circumferential stress is achieved at the outer vessel wall, whereas the maximum value of the radial stress is reached at the inner wall. The contractions of the smooth-muscle cells reduce the circumferential stretch and smooth out the heterogeneity of its distribution in the vessel wall.

Relationship between Myogenic Reaction and Autoregulation of Cerebral Circulation

Dilatation of rat pial arterioles at constant arteriolar wall strain during autoregulation of cerebral circulation was shown by the method of biomicroscopy. Wavelet-analysis of cerebral blood flow oscillations during this period revealed increased oscillation amplitude in the endothelial and neurogenic frequency ranges and unchanged amplitude at myogenic frequency range. These findings probably attest to the leading role of myogenic reaction in the autoregulation.

Age-Associated Characteristics of Vasomotor Regulation of the Pia Mater Arteries in Rats

The endothelium-dependent and myogenic reactions of pia mater arteries of the 1st-5th branching orders were studied in 1-, 3-, and 24-month-old rats by biomicroscopy method. The endothelium-independent (myogenic) reaction predominated in the 1st-3rd order branches and the endothelium-dependent vascular reaction in the 5th order branches of 3-month-old rats. Both regulatory mechanisms were equally developed in the 4th order branches. In 1-month-old rats, the endothelium-dependent reaction was more active in the majority of branches. In 24-month-old rats, this reaction was significantly higher than the endothelium-independent one only in the 4th and 5th order branches. In contrast to 3-month-old rats, the myogenic reaction of 24-month-old animals predominated in the 1st and 2nd order branches and the endothelium-dependent one in the 4th and 5th order branches. Vascular reactivity of 24-month-old rats was lower than in younger rats in all cases.

T.P.2.13 Murine embryonic stem cells injected into mdx mouse – In vivo myogenic capacity and immunogenic reaction

T.P.2.13 Murine embryonic stem cells injected into mdx mouse – In vivo myogenic capacity and immunogenic reaction

Postoperative carotid spasm in the setting of head and neck surgery

Delayed arterial spasm is a clinical and angiographic condition frequently observed after subarachnoid hemorrhage. It has long been associated with a local myogenic reaction to prolonged arterial contact with fresh blood. Carotid spasm from direct manipulation of the petrous carotid during skull base procedures is also a rare but known response to longitudinal arterial traction. Uncomplicated cervical cases, although subject to similar conditions of arterial manipulation, have less commonly been associated with arterial spasm. Two cases of severe internal carotid spasm leading to stroke in patients undergoing removal of glomus tumors are presented to emphasize carotid spasm as a potential complication in head and neck surgery. The perioperative guidelines to prevent, recognize, and treat this complication are also reviewed as outlined in the literature.

Contribution of Hindlimb Myogenic Reactions to Push-Pull Gravitational Stress in Conscious Dogs

Contribution of Hindlimb Myogenic Reactions to Push-Pull Gravitational Stress in Conscious Dogs

Structural Analysis of Heart Rhythm Spectrogram in Narcotized Cats

Eight types of peaks were revealed in the cardiac rhythm spectrum during acute experiments on vagotomized cats. Some peaks had no physiological nature and resulted from specificity of ECG processing by Fourier analysis, while others reflected myogenic reaction of the sinoatrial node (length-dependence of automaticity) to changes in venous return caused by respiratory-induced and other variations of the blood flow in the cardiovascular system.

Vasoconstriction reactions in tail artery in the rats with regional arterial hypotension

Reactivity of the tail artery to norepinephrine was studied in rats with regional arterial hypotension. Constant-flow perfusion of the artery elicited less pronounced constriction in hypotensive rats in comparison with the controls, while the constant-pressure perfusion evoked stronger vasoconstriction. This is explained by possible involvement of myogenic component in the contractile response. When myogenic reaction was inhibited by enhanced potassium concentration in the perfusion solution, vasoconstriction in hypotensive rats was less pronounced under both perfusion modes.

Endothelial Ca2+ in afferent arterioles during myogenic activity.

We measured endothelial Ca2+ concentration ([Ca2+]) in juxtamedullary afferent arterioles in response to step changes in perfusion pressure. Measurements were made with fura 2 using a fluorescence-imaging system designed to measure Ca2+ in whole tissues and minimize potentially harmful effects of ultraviolet illumination. The system yielded the typical sigmoidal relationship between fluorescence-emission ratio and [Ca2+] in vitro and was sensitive to endothelial Ca2+ transients elicited by bradykinin. Our goal was to determine whether changes in endothelial Ca2+ trigger events that cause myogenic vasoconstriction. Bradykinin, acting via endothelial cells, and sodium nitroprusside (SNP), acting independently, triggered vasodilation; bradykinin but not SNP increased endothelial Ca2+. Increased perfusion pressure caused vasoconstriction and a modest rise in endothelial Ca2+. Because the rise in Ca2+ with bradykinin initiates the vasodilation, the small rise in Ca2+ with pressure cannot cause vasoconstriction. Our results suggest that myogenic constriction is triggered from within vascular smooth muscle cells and that some other phenomenon, most likely increased shear stress, increases endothelial Ca2+ and modulates the myogenic reaction.

Length-tension dependence in vascular smooth muscle: possible participation of endothelin.

The results of experiments with isolated strips of rat portal vein, and of 'sandwich' experiments involving strips of the portal vein or aorta, revealed the involvement of endothelin in the development of myogenic reactions of the vascular smooth muscle, observed on distension of the vascular wall. Released by the endothelial cells, endothelin is capable of stimulating the contraction of these muscles.

Effect of L-arginine on myogenic reactions of vascular smooth muscle cells in hypercholesterolemia

In hypercholesterolemia, the reduced vascular response observed during stretching of the vessel wall is probably caused by disorders of endothelial functional activity. L-arginine stimulates synthetic activity of the endothelium, making it possible to use of this amino acid for correction of these impairments.

Enhanced myogenic activation in skeletal muscle arterioles from spontaneously hypertensive rats

The purpose of this study was to determine whether the vascular myogenic response is enhanced in hypertension. Experiments were conducted in the intact cremaster muscle microcirculation as well as in isolated arterioles of hypertensive (SHR) and normotensive (WKY) rats. Increasing venous pressure in vivo by approximately 5 mmHg had no effect on normotensive first- (1A) or third-order arteriolar (3A) diameters; in contrast, hypertensive 1A diameter decreased 4% (89 +/- 2 to 85 +/- 3 microns) with an 8% decrease in 3A (24 +/- 2 to 22 +/- 2 microns). To further examine this enhanced constriction to elevated intravascular pressure in SHR, diameter was monitored in isolated 1A during step increases and decreases in intraluminal pressure. Normotensive arterioles displayed myogenic responses between pressures of 50 and 170 cmH2O; in contrast, hypertensive arterioles demonstrated myogenic responses over an extended pressure range (50-210 cmH2O). In addition, the change in diameter for each step change in pressure was greater in the arterioles from SHR, indicating an increased myogenic responsiveness. The myogenic reactions were unaffected by alpha-receptor blockade with phentolamine (10(-6) M), indicating that adrenergic hypersensitivity was not involved in the enhanced response to stretch. Morphometric analysis of the vascular wall revealed no differences in wall thickness, cross-sectional wall area, or wall-to-lumen ratio between normotensive and hypertensive rats. The length-tension relationships for normotensive and hypertensive rats demonstrated that peak active tension occurred at nearly the same vascular smooth muscle length. In addition, SHR arterioles were capable of maintaining higher levels of active tension that WKY arterioles, indicating an altered length-tension curve in chronic arterial hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasoconstrictor effect of angiotensin and vasopressin in isolated rabbit afferent arterioles

The present studies were performed to examine the vasoconstrictor effect of angiotensin II (ANG II), angiotensin III (ANG III), and vasopressin in isolated afferent arterioles of the rabbit kidney. Afferent arterioles were dissected together with their glomerulus and perfused with a pressure head of 120 cmH2O. Changes in vasomotor tone were assessed as diameter changes on videotaped recordings. Afferent arterioles responded to the angiotensins and vasopressin with dose-dependent reductions in vascular diameters with half-maximum responses being observed at concentrations between 10(-9) and 10(-8) M. Responses to ANG II and III were inhibited by saralasin. Contractile responses to ANG II and vasopressin were not altered by prior occlusion of the efferent arteriole, suggesting that afferent vasoconstriction does not represent a myogenic reaction to an increase in efferent resistance. The vasoconstrictor response to ANG II was largely eliminated by removal of the glomerulus and the distal-most portion of the afferent arteriole, whereas the response to vasopressin remained intact. Our data are consistent with the notion that the juxtaglomerular apparatus (JGA) and/or glomerulus may control proximal afferent arteriolar contractility by electrotonic or myogenic coupling mechanisms or by producing cofactors that modulate vasomotor responses.

Nonuniformity of CBF response to NE- or ANG II-induced hypertension in rabbits.

The regional response of brain vasculature to moderate hypertension was investigated using two hypertensive drugs, norepinephrine (NE) and angiotensin II (ANG II), infused intravenously at low concentrations (increase in blood pressure 15-40 mm Hg). Regional cerebral blood flow (rCBF) was measured in unanesthetized and anesthetized rabbits using the [14C]ethanol saturation technique. In both groups of animals, NE and ANG II induced regional differences in the flow changes as compared with controls, confirming a regional (or segmental) heterogeneity in the regulatory mechanisms to hypertension. The responses to identical rises in blood pressure (BP) in most of the structures analyzed depended on the drug used. In the unanesthetized rabbits, the increase in vascular resistance induced by NE was greater than that induced by ANG II. With the two drugs, there was no correlation between the flow changes in any of the structures considered and either the BP increase or the BP level in unanesthetized animals. However, these flow changes were correlated with the BP increase in anesthetized animals, although differences between the effects of NE and ANG II were again observed. This study suggests that cerebrovascular regulatory mechanisms in hypertension are probably more complex than a simple myogenic reaction. Their heterogeneity and their dependence both on the cause of hypertension and on the presence of anesthetics suggest the intervention of an integrating pathway.

Active reactions of the internal carotid artery under tension

1. The vascular tone of the internal carotid artery is mainly determined by nervous control and decreases after denervation of the artery. 2. The active responses of the internal carotid artery depend on its initial tone. 3. The myogenic responses of an in situ internal carotid artery isolated from circulation upon change in the perfusion pressure are unstable. 4. Active myogenic responses to a reduction in intravascular pressure were not found in the present experiments. Upon sharp release of pressure, on the other hand, a tendency towards narrowing of the arterial lumen was found which must depend on the passive elastic properties of the walls of the internal carotid artery. 5. Marked myogenic constrictional reactions were developed by the internal carotid artery only when the intravascular pressure increased to a value exceeding the initial level by not less than 40–50%. 6. The most extensive myogenic reactions of the internal carotid artery in the present experiments in response to an increase in intravascular pressure were such as to produce a change in the vascular resistance of not more than 15–20%. 7. The duration of the myogenic reactions of the internal carotid artery to an increase in perfusion pressure did not exceed 1.0–1.5 min.

Myogenic microvascular responses to change of transmural pressure. A mathematical approach.

The recently described static and dynamic myogenic responses in the sympathectomized skeletal muscle microvessels to a given transmural pressure (PT) change applied at different rates (dPT/dt) (Grände & Mellander 1978), were further analysed in this study with a mathematical approach. The hypothesis that myogenic reactions are triggered by and related to wall tension was also tested. The mathematical model was based on a force-equilibrium in the microvessel wall including passive forces related to vascular transmural pressure, elasticity, and wall-viscosity, and active myogenic forces related to wall tension and its rate of change. Great resemblance was demonstrated between microvascular resistance curves obtained with the model and corresponding curves observed in vivo, indicating that the model quite adequately can describe myogenic microvascular resistance responses to transmural pressure stimuli. The results support the myogenic hypothesis in general and, in particular, the concept of an important rate-sensitivity in myogenic microvascular control and are compatible with the view that myogenic reactions are triggered by and related to change of wall tension. The model, in addition, provided data for certain microvascular variables which are difficult to assess by in vivo observations, e.g. Young's modulus of elasticity, wall tension, its rate of change, and internal vessel radius, and it offered a means to define more precisely the role of physical factors like effects of Poiseuille's and Laplace's laws in vascular resistance regulation.