Cerebral blood flow in vascular disease of the brain; with observations on the effects of stellate ganglion block

Cerebral endothelium-dependent function and reactivity to hypercapnia: the role of α1-adrenoreceptors

We assessed hypercapnic cerebrovascular reactivity (CVR) and endothelium-dependent function [cerebral shear-mediated dilation (cSMD)] in the internal carotid artery (ICA) with and without systemic α₁-adrenoreceptor blockade via Prazosin. We hypothesized that CVR would be reduced, whereas cSMD would remain unchanged, after Prazosin administration when compared with placebo. In 15 healthy adults (3 female, 26 ± 4 years), we conducted ICA duplex ultrasound during CVR [target +10 mmHg partial pressure of end-tidal carbon dioxide ([Formula: see text]) above baseline, 5 min] and cSMD (+9 mmHg [Formula: see text] above baseline, 30 s) using dynamic end-tidal forcing with and without α₁-adrenergic blockade (Prazosin; 0.05 mg/kg) in a placebo-controlled, double-blind, and randomized design. The CVR in the ICA was not different between placebo and Prazosin (P = 0.578). During CVR, the reactivities of mean arterial pressure and cerebrovascular conductance to hypercapnia were also not different between conditions (P = 0.921 and P = 0.664, respectively). During Prazosin, cSMD was lower (1.1 ± 2.0% vs 3.8 ± 3.0%; P = 0.032); however, these data should be interpreted with caution due to the elevated baseline diameter (+1.3 ± 3.6%; condition: P = 0.0498) and lower shear rate (-14.5 ± 23.0%; condition: P < 0.001). Therefore, lower cSMD post α₁-adrenoreceptor blockade might not indicate a reduction in cerebral endothelial function per se, but rather, that α₁-adrenoreceptors contribute to resting cerebral vascular restraint at the level of the ICA.NEW & NOTEWORTHY We assessed steady-state hypercapnic cerebrovascular reactivity and cerebral endothelium-dependent function, with and without α₁-adrenergic blockade (Prazosin), in a placebo-controlled, double-blind, and randomized study, to assess the contribution of α₁-adrenergic receptors to cerebrovascular CO₂ regulation. After administration of Prazosin, cerebrovascular reactivity to CO₂ was not different compared with placebo despite lower blood flow, whereas cerebral endothelium-dependent function was reduced, likely due to elevated baseline internal carotid arterial diameter. These findings suggest that α₁-adrenoreceptor activity does not influence cerebral blood flow regulation to CO₂ and cerebral endothelial function.

4,5 caffeoylquinic acid and scutellarin, identified by integrated metabolomics and proteomics approach as the active ingredients of Dengzhan Shengmai, act against chronic cerebral hypoperfusion by regulating glutamatergic and GABAergic synapses

Dengzhan Shengmai (DZSM) is a proprietary Chinese medicine for remarkable curative effect as a treatment of cerebrovascular diseases, such as chronic cerebral hypoperfusion (CCH) and dementia based on evidence-based medicine, which have been widely used in the recovery period of ischemic cerebrovascular diseases. The purpose of this study was to investigate the active substances and mechanism of DZSM against CCH. Integrative metabolomic and proteomic studies were performed to investigate the neuroprotective effect of DZSM based on CCH model rats. The exposed components of DZSM in target brain tissue were analysed by a high-sensitivity HPLC-MS/MS method, and the exposed components were tested on a glutamate-induced neuronal excitatory damage cell model for the verification of active ingredients and mechanism of DZSM. Upon proteomic and metabolomic analysis, we observed a significant response in DZSM therapy from the interconnected neurotransmitter transport pathways including glutamatergic and GABAergic synapses. Additionally, DZSM had a significant regulatory effect on glutamate and GABA-related proteins including vGluT1 and vIAAT, suggested that DZSM could be involved in the vesicle transport of excitatory and inhibitory neurotransmitters in the pre-synaptic membrane. DZSM could also regulated the metabolism of arachidonic acid (AA), phospholipids, lysophospholipids and the expression of phospholipase A2 in post-synaptic membrane. The results of glutamate-induced neuronal excitatory injury cell model experiment for verification of active ingredients and mechanism of DZSM showed that there are five active ingredients, and among them, 4,5 caffeoylquinic acid (4,5-CQA) and scutellarin (SG) could simultaneously affect the GABAergic and glutamatergic synaptic metabolism as well as the related receptors, the NR2b subunit of NMDA and the α1 subunit of GABA_A. The active ingredients of DZSM could regulate the over-expression of the NMDA receptor, enhance the expression of the GABA_A receptor, resist glutamate-induced neuronal excitatory damage, and finally maintain the balance of excitatory and inhibitory synaptic metabolism dominated by glutamate and GABA. Furtherly, we compared the efficacy of DZSM, 4,5-CQA, SG and the synergistic effect of 4,5-CQA and SG, and the results showed that all the groups significantly improved cell viability compared with the model group (p < 0.001). The western blot results showed that DZSM, 4,5-CQA, SG and 4,5-CQA/SG co-administration groups could significantly regulate the expression of receptors (GABA_A α1 and NR2b subunit of NMDA) and synaptic-related proteins, such as Sv2a, Syp, Slc17a7, bin1 and Prkca, respectively. These results proved DZSM and its active ingredients (4,5-CQA and SG) had the effect of regulating glutamatergic and GABAergic synapses. Finally, membrane potential FLIPR assay of 4,5-CQA and SG was used for GABRA1 activity test, and it was found that the two compounds could increase GABA-induced activation of GABRA1 receptor (GABA 10 μM) in a dose-dependent manner with EC₅₀ value of 48.74 μM and 29.77 μM, respectively. Manual patch clamp method was used to record NMDA NR1/NR2B subtype currents, and scutellarin could cause around 10 % blockade at 10 μM (p＜0.05 compared with the control group). These studies provided definitive clues of the mechanism for the neuroprotective effect of DZSM for CCH treatment and the active compounds regulating glutamatergic and GABAergic synapses. Additionally, 4,5-CQA and SG might be potential drugs for the treatment of neurodegenerative disease related to CCH.

Regulation of cerebral blood flow and metabolism during exercise

NEW FINDINGS

What is the topic of this review? The manuscript collectively combines the experimental observations from >100 publications focusing on the regulation of cerebral blood flow and metabolism during exercise from 1945 to the present day. What advances does it highlight? This article highlights the importance of traditional and historical assessments of cerebral blood flow and metabolism during exercise, as well as traditional and new insights into the complex factors involved in the integrative regulation of brain blood flow and metabolism during exercise. The overarching theme is the importance of quantifying cerebral blood flow and metabolism during exercise using techniques that consider multiple volumetric cerebral haemodynamics (i.e. velocity, diameter, shear and flow). Cerebral function in humans is crucially dependent upon continuous oxygen delivery, metabolic nutrients and active regulation of cerebral blood flow (CBF). As a consequence, cerebrovascular function is precisely titrated by multiple physiological mechanisms, characterized by complex integration, synergism and protective redundancy. At rest, adequate CBF is regulated through reflexive responses in the following order of regulatory importance: fluctuating arterial blood gases (in particularly, partial pressure of carbon dioxide), cerebral metabolism, arterial blood pressure, neurogenic activity and cardiac output. Unfortunately, the magnitude that these integrative and synergistic relationships contribute to governing the CBF during exercise remains unclear. Despite some evidence indicating that CBF regulation during exercise is dependent on the changes of blood pressure, neurogenic activity and cardiac output, their role as a primary governor of the CBF response to exercise remains controversial. In contrast, the balance between the partial pressure of carbon dioxide and cerebral metabolism continues to gain empirical support as the primary contributor to the intensity-dependent changes in CBF observed during submaximal, moderate and maximal exercise. The goal of this review is to summarize the fundamental physiology and mechanisms involved in regulation of CBF and metabolism during exercise. The clinical implications of a better understanding of CBF during exercise and new research directions are also outlined.

Integrative regulation of human brain blood flow

Herein, we review mechanisms regulating cerebral blood flow (CBF), with specific focus on humans. We revisit important concepts from the older literature and describe the interaction of various mechanisms of cerebrovascular control. We amalgamate this broad scope of information into a brief review, rather than detailing any one mechanism or area of research. The relationship between regulatory mechanisms is emphasized, but the following three broad categories of control are explicated: (1) the effect of blood gases and neuronal metabolism on CBF; (2) buffering of CBF with changes in blood pressure, termed cerebral autoregulation; and (3) the role of the autonomic nervous system in CBF regulation. With respect to these control mechanisms, we provide evidence against several canonized paradigms of CBF control. Specifically, we corroborate the following four key theses: (1) that cerebral autoregulation does not maintain constant perfusion through a mean arterial pressure range of 60-150 mmHg; (2) that there is important stimulatory synergism and regulatory interdependence of arterial blood gases and blood pressure on CBF regulation; (3) that cerebral autoregulation and cerebrovascular sensitivity to changes in arterial blood gases are not modulated solely at the pial arterioles; and (4) that neurogenic control of the cerebral vasculature is an important player in autoregulatory function and, crucially, acts to buffer surges in perfusion pressure. Finally, we summarize the state of our knowledge with respect to these areas, outline important gaps in the literature and suggest avenues for future research.

[Idiopathic orthostatic hypotension (Shy-Drager syndrome). Results of regional cerebral blood flow measurements (author's transl)]

Using a gamma camera and the stochastic method, regional cerebral blood flow was measured in a patient with the diagnosis of idiopathic orthostatic hypotension. Blood pressure was altered by tilting the patient in supine position head-up and head-down. A partial defect in the autoregulation and CO2 sensitivity was found. Sensitivity to Norepinephrine was checked by intravenous infusion of 0.02 mug/min/kg body weight. An immediate marked rise in blood pressure was observed. Clinical symptoms, therapeutic guidelines, and histopathological findings are discussed.

[Stellate ganglion block under EEG control in the treatment of complicated cervical migraine (author's transl)]

Complicated migraine is regarded as a cerebrovascular syndrome of functional character. In the case of a young man with cervical migraine associated with paroxysmal neurological disorders and persisting EEG abnormalities, stellate ganglion blocks were performed under EEG control. A transient amelioration of the pathological EEG pattern was observed after each stellate ganglion block and after several treatments the EEG was normal and the migraine attacks disappeared. The pathophysiology of the effect of stellate ganglion block on cerebral blood flow is discussed.

Cerebrospinal fluid pH and monoamine and glucolytic metabolites in Alzheimer's disease

Determinations of acid monoamine metabolites, such as homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), in cerebrospinal fluid (CSF) give valid information on the metabolism of the corresponding amines in the brain tissue (Moir et al., 1970; Roos, 1970). The monoamine metabolites in the CSF are related to age. The concentrations of HVA and 5-HIAA increase with age (Gottfries et al., 1971). Probenecid blocks the elimination of HVA and 5-HIAA from brain tissue to blood (Neff et al., 1964, 1967; Werdinius, 1966) and from CSF to blood (Guldberg et al., 1966; Olsson and Roos, 1968). Probenecid thus normally induces an increase in the concentrations of the acid monoamine metabolites in the CSF, which is related to the turnover of monoamines in the brain tissue.

Cerebrovascular regulation in preganglionic and postganglionic autonomic insufficiency

Cerebral blood flow was measured in four subjects with chronic idiopathic autonomic insufficiency using 85 Kr inhalation, cerebral A-V samples for scintillation counting, and O 2 content determination. Blood pressure was varied by up or down tilting and L-norepinephrine infusion. In three patients with typical Shy-Drager syndrome and preganglionic denervation, CBF regulation to pressure and Pa CO CO 2 change was intact. In a fourth patient with postganglionic denervation, CBF autoregulation was absent to changes in blood pressure but was preserved normally to increases or decreases in Pa CO CO 2 CBF and CMRO 2 , at rest were normal (52.6 cc and 3.1 cc). Hyperventilation to Pa CO CO 2 34.3 mm failed to restore autoregulation to increased blood pressure. The results imply a functional role for postganglionic autonomic fibers in CBF autoregulation.

Unresponsiveness of pial precapillary vessels to catecholamines and sympathetic nerve stimulation

A systematic analysis of the possible existence of neurogenic control of precapillary pial vessels was made in three species (cat, dog, and rabbit). In all of these animals, pial vessels failed to respond to externally applied isoproterenol or norepinephrine in high concentrations (up to 100 µg/ml), although the vessels did dilate in response to externally applied histamine. Adrenergic nerve endings on the pial vessels were demonstrated by fluorescent histochemical techniques specific for catecholamines. However, in the absence of changes in arterial blood pressure and arterial blood carbon dioxide tension, pial precapillary vessels showed no change in caliber in response to stimulation of the ipsilateral superior cervical ganglion. These results show that pial precapillary vessels are not subject to vasoconstriction probably because they lack sufficient receptors for the catecholamine neurotransmitter.

Relationship of serial measurements of cerebral hemodynamics to prognosis in patients with hypertension and cerebrovascular disease

Baseline and follow-up measurements of cerebral hemodynamics were performed in hypertensive patients by the N 2 O method with a certain time interval. A tendency for some decrease in the CBF was noted, but the difference was not statistically significant.

Twelve hypertensive patients suffered from a stroke during the period of observation. The CBF values prior to the stroke varied so widely that there was no predictive value from these measurements.

The decrease in CBF in a mild case of cerebral infarction is slight and is followed by little fluctuation. The decrease in a case of moderate severity is marked but returns to normal in two to five months. Clinically severe cases of infarction and hemorrhage are also characterized by a marked decrease in CBF, but this decrease of infarcted cases may be irreversible.

A higher incidence of recurrent infarction is noted in those patients in whom recovery of CBF following a stroke is poorest. This is most apparent in those patients suffering a recurrence within one year.

Cerebral cortex perfusion rates in dementia

Cerebral cortex perfusion rates (CPR) were measured in 11 patients with dementia. In six patients the dementia appeared to be due to a primary neuronal degeneration and in the remainder it appeared to be secondary to vascular disease. In the context of blood flow measurement, it is suggested that the terms primary and secondary dementia are preferable to the terms presenile and senile dementia, because the latter are classified by age alone and the terms have no aetiological or pathological significance. The perfusion rates in patients with primary dementia were within normal limits for their age, whereas those in patients with secondary dementia were significantly reduced. This difference is likely to apply only if the measurements are made early in the course of the disease.

Cerebral blood flow and metabolism in the Wernicke-Korsakoff syndrome

Cerebral blood flow and metabolism were measured by the iodoantipyrine-4-(131)I method in nine patients and by the nitrous oxide method in three patients with the Wernicke-Korsakoff syndrome.Cerebral blood flow and cerebral oxygen and glucose consumption were strikingly reduced from the normal, whereas cerebral vascular resistance was increased. Total cerebral metabolism and blood flow may be greatly reduced even though the cerebral metabolic defect is confined to circumscribed anatomical areas. Profound reduction in brain metabolism is not necessarily reflected in alterations of consciousness or awareness as has been previously suggested, or in electroencephalographic abnormalities. This appears to provide cogent support for the neurophysiological principle that disturbance of consciousness is a function of the location of the lesion, not the over-all degree of metabolic defect. The absence of improvement of cerebral metabolic functions in two patients who were restudied after an additional 2 to 3 weeks of treatment confirms the clinical impression of incomplete recovery in many such patients.

Effect of nitroglycerin on the coronary circulation in patients with coronary artery disease or increased left ventricular work

Except for the electrocardiogram objective evaluation of the functional state of the coronary circulation in man is often difficult. The nature of the coronary circulation in the presence of known coronary insufficiency has not been evaluated. In this report, 17 patients were studied of whom 14 had angina pectoris. Observations were made of coronary blood flow and hemodynamics both at rest and following administration of nitroglycerin. The authors conclude that resting coronary flow is normal, but cannot increase further with dilators. They consider this phenomenon a consequence of prior exhaustion of the dilator capacity of the arterioles in compensation for the atherosclerotic obstruction of the coronary tree. The "fixed flow" concept is suggested as an objective means of detecting coronary insufficiency. Nitrites probably relieve pain in some manner other than general coronary dilatation.