Volhard Lecture. Brain, blood pressure and stroke

Chronic infusion of epigallocatechin-3-O-gallate into the hypothalamic paraventricular nucleus attenuates hypertension and sympathoexcitation by restoring neurotransmitters and cytokines

Reactive oxygen species (ROS) in the brain are involved in the pathogenesis of hypertension. Epigallocatechin-3-O-gallate (EGCG), one of the active compounds in green tea, has anti-oxidant, anti-inflammatory and vascular protective properties. This study was designed to determine whether chronic infusion of EGCG into the hypothalamic paraventricular nucleus (PVN) attenuates ROS and sympathetic activity and delays the progression of hypertension by up-regulating anti-inflammatory cytokines, reducing pro-inflammatory cytokines (PICs) and decreasing nuclear factor-kappa B (NF-κB) activity, as well as restoring the neurotransmitters balance in the PVN of spontaneously hypertensive rats (SHR). Adult normotensive Wistar-Kyoto (WKY) rats and SHR received bilateral PVN infusion of EGCG (20μg/h) or vehicle via osmotic minipumps for 4 weeks. SHR showed higher mean arterial pressure, plasma proinflammatory cytokines and circulating norepinephrine (NE) levels compared with WKY rats. SHR also had higher PVN levels of the subunit of NAD(P)H oxidase (gp91^phox), ROS, tyrosine hydroxylase, and PICs; increased NF-κB activity; and lower PVN levels of interleukin-10 (IL-10) and 67kDa isoform of glutamate decarboxylase (GAD67) than WKY rats. PVN infusion of EGCG attenuated all these changes in SHR. These findings suggest that SHR have an imbalance between excitatory and inhibitory neurotransmitters, as well as an imbalance between pro- and anti-inflammatory cytokines in the PVN. Chronic inhibition of ROS in the PVN restores the balance of neurotransmitters and cytokines in the PVN, thereby attenuating hypertensive response and sympathetic activity.

Brain function, cognition, and the blood pressure response to pharmacological treatment

OBJECTIVE

To extend evidence suggesting that essential hypertension influences neuropsychological performance and that brain function before treatment is related to the success of pharmacological lowering of blood pressure (BP).

METHODS

A voxel-based examination of the whole brain was conducted among 43 hypertensive patients treated for 1 year with assessment pre and post treatment, using positron emission tomography and neuropsychological testing.

RESULTS

Neuropsychological performance improved over the year of treatment but was unrelated to change in regional cerebral blood flow (rCBF). Neither mean resting rCBF nor responsivity to a working memory task changed significantly with treatment. However, patients with greater lowering of systolic BP during treatment showed increased rCBF responsivity to a working memory task in medial and orbital frontal areas and decreased rCBF responsivity in mid frontal, parietal, thalamus, and pons (as well as lower thalamic rCBF pretreatment). Improved working memory performance over the treatment period was related to decreased responsivity in medial frontal, medullary, and parietal areas. Patients showing greater lowering of BP with treatment seemed to reduce excitatory and enhance inhibitory coupling between memory processing and BP more than those with less treatment success.

CONCLUSION

Degree of treatment success for both BP and cognitive performance among hypertensives is related to differing patterns of rCBF. Overall, the results emphasize the relevance of brain function to the treatment of hypertension.

Effect of acute and chronic hypertension on short- and long-term spatial and avoidance memory in male rats

It has been demonstrated that hypertension can lead to coronary heart disease, heart failure, stroke, and memory loss. In this study we investigated the effect of acute and chronic hypertension on the avoidance and spatial learning and memory in rats. The forty male rats were divided into acute hypertensive, chronic hypertensive and control for each group rats. Hypertension was induced by Deoxy Corticosterone Acetate (DOCA)-salt method. DOCA was injected 30mg/kg of body weight subcutaneously, twice a week. These rats received NaCl 1% instead of tap water for drinking throughout the experiment. The control group received normal saline injection with usual drinking water. Spatial learning and memory was investigated by Morris water maze test and passive avoidance learning by Shuttle box test in the rats after hypertension induction. Results showed that acute hypertension impaired short-term memory in passive avoidance learning. However, acute and chronic hypertension did not affect spatial learning and memory. These data suggest that simple uncomplicated hypertension does not remarkably alter cognition.

Effect of deep brain stimulation of the posterior hypothalamic area on the cardiovascular system in chronic cluster headache patients

The objective of this study was to determine the cardiovascular effects of chronic stimulation of the posterior hypothalamic area (PHA) in cluster headache (CH) patients. Systolic and diastolic blood pressure (SBP, DBP), cardiac output, total peripheral resistance (TPR), heart rate (HR) and breathing were monitored at supine rest and during head-up tilt test (HUTT), Valsalva manoeuvre, deep breathing, cold face test and isometric handgrip in eight drug-resistant chronic CH patients who underwent monolateral electrode implantation in the PHA for therapeutic purposes. Autoregressive power spectral analysis (PSA) of HR variability (HRV) was calculated at rest and during HUTT. Each subject was studied before surgery (condition A) and after chronic deep brain stimulation (DBS) of PHA (condition B). Baseline SBP, DBP, HR and cardiovascular reflexes were normal and similar in both conditions. With respect to condition A, DBP, TPR and the LF/HF obtained from the PSA of HRV were significantly (P < 0.05) increased during HUTT in condition B. In conclusion, chronic DBS of the PHA in chronic CH patients is associated with an enhanced sympathoexcitatory drive on the cardiovascular system during HUTT.

The challenge of blood pressure management in neurologic emergencies

Hypertensive crises are commonly seen in the emergency department, and acute stroke is often the inciting etiology of a hypertensive crisis. Cerebral autoregulation is disrupted in acute stroke, and efforts to lower blood pressure may reduce cerebral perfusion and worsen outcomes. Although most patients with stroke have elevated blood pressure, evidence from clinical trials to guide therapy are scarce. Current national guidelines recommend lowering blood pressure after stroke only if end-organ damage is present or if systolic/diastolic blood pressures exceed 220/120 or 185/110 mm Hg in patients ineligible and in those eligible to receive thrombolytic drug therapy, respectively. Recommended pharmacologic interventions for elevated blood pressure after acute ischemic stroke include labetalol, nicardipine, or nitroprusside, depending on the severity of the elevation. Similar recommendations have been made for intracerebral hemorrhage. Subarachnoid hemorrhage is managed with nimodipine and other calcium channel blockers to prevent vasospasm and improve clinical outcomes. Data from ongoing clinical trials may improve guidance about the management of elevated blood pressure after acute stroke.

Hypothalamic cardiovascular effects of angiotensin-(1–7) in spontaneously hypertensive rats

The objective of the present work was to study the cardiovascular actions of the intrahypothalamic injection of Ang-(1-7) and its effects on the pressor response to Ang II in spontaneously hypertensive (SH) rats and Wistar Kyoto (WKY) animals. In anaesthetized SH and WKY rats, a carotid artery was cannulated for mean arterial pressure (MAP) measurement and a stainless-steel needle was inserted into the anterior hypothalamus for drug administration. The cardiovascular effects of the intrahypothalamic administration of Ang-(1-7) were determined in SH and WKY rats. In SH rats, the effect of irbesartan and D-Ala-Ang-(1-7) on Ang-(1-7) cardiovascular effect was also evaluated. Ang II was administered in the hypothalamus of SH and WKY rats and changes in blood pressure and heart rate were measured followed by the administration of Ang II, Ang II+Ang-(1-7) or Ang II+D-Ala-Ang-(1-7). Ang-(1-7) did not the change basal MAP in WKY rats, but induced a pressor response in SH animals. Whilst the co-administration of D-Ala-Ang-(1-7) did not affect the response to Ang-(1-7), the previous administration of irbesartan prevented the effect of the peptide. The intrahypothalamic injection of Ang II induced a significantly greater pressor response in SH animals compared to normotensive rats. The co-administration of Ang-(1-7) with Ang II did not affect the pressor response to Ang II in the WKY group. In SH rats, whilst the co-administration of Ang-(1-7) with Ang II reduced the pressor response to Ang II, the concomitant application of D-Ala-Ang-(1-7) with Ang II increased the pressor response to the octapeptide after 5 and 10 min of intrahypothalamic administration. In conclusion, our result demonstrated that the biologically active peptide Ang-(1-7) did not participate in the hypothalamic blood pressure regulation of WKY animals. In SH rats, Ang-(1-7) exerted pleiotropic effects on blood pressure regulation. High dose of the heptapeptide produced a pressor response because of an unspecific action by activation of AT1 receptors. The concomitant administration of lower doses of Ang-(1-7) with Ang II reduced the pressor response to the octapeptide. Finally, the effect of AT(1-7) antagonist on Ang II pressor response suggested that hypothalamic formed Ang-(1-7) are implicated in the regulation of the cardiovascular effects of Ang II.

Anterior hypothalamic beta-adrenoceptors in chronic aortic-coarctated hypertensive rats: An interaction with central angiotensin II receptors

1. The aim of the present study was to investigate the activity of anterior hypothalamic beta-adrenoceptors and angiotensin (Ang) II receptors on blood pressure in normotensive rats and aortic-coarctated (ACo) animals at a chronic stage of hypertension. A possible interaction between beta-adrenoceptors and AngII pressor activity was also investigated. 2. Injection of isoproterenol (0.1-10 nmol) in the anterior hypothalamic area induced a dose-dependent decrease in mean arterial pressure (MAP) in sham-operated (SO), but not in ACo, animals. Isoproterenol (1 nmol) reduced blood pressure in SO rats (DeltaMAP -10.1+/-1.4 mmHg; n=10) but not in ACo animals (DeltaMAP -0.9+/-1.6 mmHg; n=10; P<0.05 vs SO rats). Whereas previous administration of atenolol (40 nmol) enhanced the cardiovascular effect of isoproterenol (1 nmol) in ACo rats but not in SO animals, propranolol (40 nmol) prevented the hypotensive action of isoproterenol in both experimental groups. Intrahypothalamic administration of clenbuterol decreased MAP in a dose-dependent manner; however, the depressor response to clenbuterol (10 nmol) was greater in ACo rats than in SO rats (DeltaMAP -26.8+/-3.2 vs -14.4+/-2.4 mmHg, respectively; n=5 for both; P<0.05). When AngII (50 ng) was injected into the anterior hypothalamic area, a greater pressor response was observed in ACo rats than in SO rats (DeltaMAP 19.6+/-1.1 vs 11.3+/-0.6 mmHg, respectively; n=5 for both; P<0.05). Atenolol (40 nmol) pretreatment partially and significantly prevented the pressor response to AngII in ACo rats, but not in SO rats. 3. In conclusion, these results provide pharmacological evidence for the existence of a beta1-adrenoceptor-mediated pressor mechanism in the anterior hypothalamic area of ACo rats that is absent in SO rats. The enhanced depressor beta2-adrenoceptor activity observed in chronic ACo rats could be a compensatory adjustment to pressor beta1-adrenoceptor activity. Conversely, pressor overactivity of AngII was observed in the anterior hypothalamic area of ACo rats at a chronic hypertensive stage; this enhancement could be explained, at least in part, by the pressor beta1-adrenoceptor activity.

Role of alpha2-adrenergic receptors and cyclic adenosine monophosphate-dependent protein kinase in the regulation of norepinephrine release in the central nervous system of spontaneously hypertensive rats

There has been much evidence showing that the central sympathetic nervous system may be involved in the control of blood pressure. In the present study, we investigated the role of the presynaptic alpha2-adrenergic receptors and the cyclic adenosine monophosphate-dependent protein kinase (protein kinase A) in the regulation of norepinephrine release in the central nervous system in hypertension. The alpha2-adrenergic receptor agonists UK 14, 304 and clonidine inhibited the stimulation-evoked [3H]norepinephrine release in a dose-dependent manner in the medulla oblongata of Sprague-Dawley rats. Pretreatment of pertussis toxin (a potent inhibitor of the Gi-protein) attenuated the suppression of NE release by UK 14, 304. The protein kinase A inhibitor H-8 also reduced the stimulation-evoked [3H]norepinephrine release in rat medulla oblongata. In spontaneously hypertensive rats, the inhibitory effect of UK 14, 304 on the stimulation-evoked norepinephrine release was significantly less than in age-matched normotensive Wistar-Kyoto rats. By contrast, the protein kinase A inhibitor H-8 reduced the stimulation-evoked norepinephrine release to a greater extent in hypertension than in normotensive controls. The results of the present study showed that the alteration in the presynaptic alpha2-receptor-protein kinase A system might actively participate in the regulation of norepinephrine release in the central nervous system in hypertension.

Viral vectors as tools for studies of central cardiovascular control

During the last few years physiological genomics has been the most rapidly developing area of physiology. Given the current ease of obtaining information about nucleotide sequences found in genomes and the vast amount of readily available clones, one of the most pertinent tasks is to find out about the roles of the individual genes and their families under normal and pathological conditions. Viral gene delivery into the brain is a powerful tool, which can be used to address a wide range of questions posed by physiological genomics including central nervous mechanisms regulating the cardio-vascular system. In this paper, we will give a short overview of current data obtained in this field using viral vectors and then look critically at the technology of viral gene transfer.

Involvement of gamma-aminobutyric acid (GABA) B receptors in the hypotensive effect of systemically administered GABA in spontaneously hypertensive rats

We investigated the effects of intraduodenally (i.d.) administered gamma-aminobutyric acid (GABA) on blood pressure (BP) in anesthetized spontaneously hypertensive rats (SHR) and the mechanism underlying this effect, especially the type of GABA receptor involved in the depressive effect of this amino acid. GABA (0.3 to 300 mg/kg, i.d.) caused a dose-related decrease in the BP of 9.20 +/- 3.96 to 35.0 +/- 5.34 mmHg (mean +/- S.E.M.) that lasted for 30 to 50 min. The minimum effective i.d. dose of GABA was 0.3 to 1.0 mg/kg. Results pertaining to the mechanism underlying the GABA-induced effects on BP were as follows: a) GABA did not alter the BP-related effects of exogenous noradrenaline and acetylcholine; b) pretreatment with hexamethonium decreased the GABA-induced fall in BP, and GABA tended to reduce the pressor response associated with injection of dimethyl phenylpiperazinium; and c) pretreatment with 2-hydroxysaclofen markedly reduced the GABA-induced drop in BP, whereas pretreatment with bicuculline did not. In conclusion, in SHR, low-dose (0.3 to 1.0 mg/kg, i.d.) GABA had a hypotensive effect, which may result from attenuation of sympathetic transmission through the activation of GABA(B) receptors at presynaptic or ganglionic sites.

Progress in reducing the burden of stroke

1. The burden of stroke worldwide is growing rapidly, driven by an ageing population and by the rapid rate of urbanization and industrialization in the developing world. There are approximately 5 million fatal and 15 million non-fatal strokes each year and over 50 million survivors of stroke alive, worldwide, today. 2. The most important determinant of stroke risk is blood pressure, with a strong, continuous relationship between the level of the systolic and diastolic pressures and the risk of initial and recurrent stroke, in both Western and Asian populations. 3. Randomized clinical trials have clearly demonstrated that blood pressure lowering reduces the risk of initial stroke by 35-40% in hypertensive patients; but, until recently, there was no conclusive evidence that blood pressure lowering was effective in the secondary prevention of stroke. 4. The Perindopril Protection Against Recurrent Stroke Study (PROGRESS) has provided definitive evidence that blood pressure lowering in patients with previous stroke or transient ischaemic attack (TIA) reduces the incidence of secondary stroke by 28%, of major vascular events by 26% and of major coronary events by 26%. These reductions were all magnified by approximately 50% in a subgroup of patients in whom the angiotensin-converting enzyme inhibitor perindopril was routinely combined with the diuretic indapamide. 5. Successful global implementation of a treatment with perindopril and indapamide in patients with a history of stroke or TIA would markedly reduce the burden of stroke and could avert between 0.5 and one million strokes each year, worldwide.

Spontaneously hypertensive rats exhibit altered cardiovascular and neuronal responses to muscle contraction

We examined the cardiovascular and ventrolateral medullary neuronal responses to muscle contraction in the spontaneously hypertensive rat (SHR) and normotensive Wistar-Kyoto rat (WKY) control. Cardiovascular, respiratory and ventrolateral medullary neuronal responses to muscle contraction evoked by tibial nerve stimulation were recorded. SHRs exhibited significantly larger drops in arterial pressure compared to WKYs in response to muscle contraction (P < 0.05). Basal ventrolateral medulla neuronal discharge rates were similar between the SHR and the WKY groups. A majority of neurons recorded responded to muscle contraction in both the WKY (77 %; n = 53) and the SHR groups (68 %; n = 62). There was no difference in the percentage of neurons that responded with an increase (approximately 60 %) or decrease (approximately 40 %) in firing rate between hypertensive and normotensive rats. Pulse wave-triggered averaging techniques showed that most neurons that responded to muscle contraction also possessed a basal firing rhythm temporally related to the cardiac cycle (85 % in WKYs, 83 % in SHRs). However, decreases in neuronal firing rates in response to muscle contraction were significantly greater in SHRs than WKYs. Therefore, we conclude that muscle contraction unmasks a hyperexcitability of neurons in the ventrolateral medulla of SHRs that parallels the heightened blood pressure responses.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

Chronic, severe hypertension does not impair spatial learning and memory in Sprague-Dawley rats

This study tested the hypothesis that long-term hypertension impairs spatial learning and memory in rats. In 6-wk-old Sprague-Dawley rats, chronic hypertension was induced by placing one of three sizes of stainless steel clips around the descending aorta (above the renal artery), resulting in a 20-80-mm Hg increase of arterial pressure in all arteries above the clip, that is, the upper trunk and head. Ten months later, the rats were tested for 5 d in a repeated-acquisition water maze task, and on the fifth day, they were tested in a probe trial; that is, there was no escape platform present. At the end of the testing period, the nonsurgical and sham control groups had similar final escape latencies (16 +/- 4 sec and 23 +/- 9 sec, respectively) that were not significantly different from those of the three hypertensive groups. Rats with mild hypertension (140-160 mm Hg) had a final escape latency of 25 +/- 6 sec, whereas severely hypertensive rats (170-199 mm Hg) had a final escape latency of 21 +/- 7 sec and extremely hypertensive rats (>200 Hg) had a final escape latency of 19 +/- 5 sec. All five groups also displayed a similar preference for the correct quadrant in the probe trial. Together, these data suggest that sustained, severe hypertension for over 10 mo is not sufficient to impair spatial learning and memory deficits in otherwise normal rats.